HOUSE OF LORDS
 AC 824
3 May 1972
LORD WILBERFORCE, VISCOUNT DILHORNE, LORD PEARSON, LORD CROSS OF CHELSEA AND LORD SALMON
F M Drake QC, H K Goddard and Douglas Hogg for the appellants
Iain Glidewell QC and D G Nowell for the respondent
LORD WILBERFORCE: My Lords, the enactment under which the appellants have been convicted is the Rivers (Prevention of Pollution) Act 1951. The relevant words are 'if he cause sor knowingly permits to enter a stream any poisonous, noxious or polluting matter'.
The subsection evidently contemplates two things -- causing, which must involve some active operation or chain of operations involving as the result the pollution of the stream; knowingly permitting, which involves a failure to prevent the pollution, which failure, however, must be accompanied by knowledge. I see no reason either for reading back the word 'knowingly' into the first limb, or for reading the first limb as, by deliberate contrast, hitting something which is unaccompanied by knowledge. The first limb involves causing and this is what has to be interpreted.
In my opinion, 'causing' here must be given a common sense meaning and I depreciate the introduction of refinements, such as causa causans, effective cause or novus actus. There may be difficulties where acts of third persons or natural forces are concerned but I find the present case comparatively simple. The appellants abstract water, pass it through their works where it becomes polluted, conduct it to a settling tank communicating directly with the stream, into which the polluted water will inevitably overflow if the level rises over the overflow point. They plan, however, to recycle the water by pumping it back from the settling tank into their works; if the pumps work properly this will happen and the level in thank will remain below the overflow point. It did not happen on the relevant occasion due to some failure in the pumps.
In my opinion, this is a clear case of causing the polluted water to enter the stream. The whole complex operation which might lead to this result was an operation deliberately conducted by the appellants and I fail to see how a defect in one stage of it, even if we must assume that this happened without heir negligence, can enable them to say they did not cause the pollution. In my opinion, complication of this case by infusion of the concept of mens rea, and its exceptions, is unnecessary and undesirable. The section is clear, its application plain. I agree with the majority of the Divisional Court who upheld the conviction, except that rather than say that the actions of the appellants were a cause of the pollution I think it more accurate to say that the appellants caused the polluting matter to enter the stream.
There are two previous decisions which call for brief comment. The first is Moses v Midland Railway Co (1915) 113 LT 451 which was decided on similar terminology in s 5 of the Salmon Fishery Act 1861. The cause of the escape of the polluting creosote was a defective tap in the tank wagon which did not belong to the railway company but to a private owner. The conclusion that the railway company had not caused it to flow was, I should have thought, inevitable. The second is Impress (Worcester) Ltd v Rees  2 All ER 357. The appellants had placed a fueloil tank near, although not adjacent to, the River Severn.The oil escaped through a valve which was not kept locked.The Divisional Court found that it was an inevitable conclusion of fact that some unauthorised person had opened the valve for purposes unconnected with the appellants' business. They held that the opening of the valve was of so powerful a nature that the conduct of the appellants was not a cause of the flow of oil. I do not desire to question this conclusion, but it should not be regarded as a decision that in every case the act of a third person necessarily interrupts the chain of causation initiated by the person who owns or operates the installation or plant from which the flow took place. The answer to such questions is one of degree and depends on a proper attribution of responsibility for the flow of the polluting matter.
The actual question submitted to this House under the Administration of Justice Act 1961, s (2) is:
'Whether the offence of causing polluting matter to enter a stream contrary to Section 2 of the Rivers (Prevention of Pollution) Act 1951 can be committed by a person who has no knowledge of the fact that polluting matter is entering the stream and has not been negligent in any relevant respect.'
The answer to this, I suggest, should be 'Yes', it being understood that the test is whether the person concerned caused or knowingly permitted the poisonous, noxious or polluting matter to enter the stream. As, in my opinion, the appellants did so cause, I would dismiss the appeal.
VISCOUNT DILHORNE: My Lords, the the appellants, Alphacell Ltd, were convicted by the justices at Radcliffe in Lancashire on an information that they had caused polluting matter to enter the River Irwell contrary to s 2(1) of the Rivers (Prevention of Pollution) Act 1951.
At their Mount Sion works, which are on the bank of the river, the appellants treated manilla fibres as part of the process of manufacturing paper. The fibres had to be boiled and the water in which they were boiled became seriously polluted. It was drained into tanks from which it was removed by road tankers. There was also a washing process and the water used in the washing process was drained into two settling tanks situated on the edge of the river. One settling tank was higher than the other and the overflow from the higher tank went into the lower. In a shed above the lower tank there were two pumps with pipes extending downwards into the liquid in the lower tank, through which the water was sucked and pumped back into a reservoir from which it could be taken and, after filtration, used again.
If the pumps worked properly, there should have been no overflow from the lower tank, but if that tank did overflow, the liquid flowing from it went straight into a channel, provided for the purpose, which led straight into the river. So if the pumps for some reason failed to operate properly, the system instituted by the appellants made provision for any overflow to go straight into the river.
One of the two pumps worked automatically, coming into operation when the water in the lower tank reached a certain level and switching itself off when the level dropped three feet three inches below the level at which it would overflow into the river. The other pump was manually operated.
Evidence was given by a consultant of the paper trade, a Mr Evans, who had been concerned with the planning of the circulation of the water. He said that one pump was sufficient to keep the liquid from overflowing it nothing went wrong, and that the second pump was there is case anything went wrong with the first.
At 4.30 pm on Tuesday, 25th November 1969, an assistant inspector employed by the Mersey and Weaver River Authority saw that liquid was overflowing from the lower tank into the river at the rate, he estimated, of 250 gallons an hour. Both pumps were then working. He took samples, analysis of which showed that the liquid being discharged had a biological oxygen demand of 160 milligrammes per litre. The river authority only permitted the discharge of an effluent with a biological oxygen demand not exceeding 20 milligrammes perlitre.
Each of the pipes which carried the water to the pumps was fitted with a rose to prevent foreign matter being sucked into the pump. The holes in each rose were 3/4 inch in diameter.
Mr Atkinson, a foreman employed by the appellants, testified that on 25th November he had inspected the tanks at 8.15 am and that on pump was operating then. He inspected the tanks at 11.15 am and saw that the level in the lower tank was rising so he switched on the second pump. He made another inspection at 1.15 pm and did not notice any difference in the level. He came back again at 3.45 pm and the level in the tank was the same despite the fact that both pumps had been operating since 11.15 am.
If Mr Atkinson knew that if nothing was wrong, one pump was sufficient to cope with the flow and to prevent an overflow, he surely should have suspected that something was seriously wrong when he found that both pumps operating for several hours had not lowered the level of the water.
A fitter employed by the appellants, a Mr Courtney, stated that he had inspected and emptied the roses at the end of the pipes every weekend and that both pumps had been inspected by him during the weekend before 25th November. He said that he had been inspected the impellers to the pumps and had got his fingers in the vents.
After the samples were taken the pumps were stopped and dismantled. It was then found that brambles, ferns and longleaves were wrapped around each impeller and that the vents of both pipes were blocked. Mr Courtney said that he had installed the pumps and had been employed there ever since and that he had never before found such things in the pumps.
If it be the case that the pumps were properly inspected during the weekend and were then in proper order, the brambles and leaves must have got into the impellers on the Monday and Tuesday and, if the roses at the end of each pipe were in place, have been sucked through the 3/4 inch holes in the roses. It sounds improbable that this should have happended with both pumps in so short a time to such a degree that both pumps were blocked but one does not know, for the case stated does not reveal, what conclusion, if any, the justices came to about this.
The case stated is unfortunately in an unsatisfactory from. In para 2 the justices said that they found the following facts. One would expect that to be followed by a statement of the facts found, that is to say, the conclusions on questions of fact to which the justices had come after hearing the evidence. But para 3 of the case merely sets out the evidence the justices had heard and not their conclusions thereon. Merely to set out the justices had heard and not their conclusions thereon. Merely to set out the evidence is no substitute for findings of fact.
Paragraph 3 records that one witness said that the appellants had taken all reasonable steps to make sure that water did not escape into the river. Did the justices accept this evidence and find as a fact that all reasonable steps had been taken or did they not do so? The case stated leaves that uncertain and were it not for the fact that it is possible to reach a conclusion in this appeal without knowing whether that had or had not been found, I would have been in favour of the case being sent back to the justices to be properly stated.
The respondent, so the case states, contended that the appellants had caused polluting matter to enter the river and that they --
'had not done everything in their power to ensure that the machinery which should ensure that the tanks should not allow any overflow into the river had not worked efficiently [sic].'
Presumably what was meant was that they had not done everything to ensure that it had not worked inefficiently.
The justices in the paragraph numbered 7 in the case (in fact para 8) said that they were --
'of the opinion that the Appellants had caused the polluting matter to enter the River by their failure to ensure that the apparatus was maintained in a satisfactory condition to do the job for which it was provided.'
One does not know whether they were of the opinion that that failure was due to negligence on the part of the appellants, or their servants or whether it was their view that the appellants had caused the overflow without negligence as they had installed a system which was bound to lead to an overflow if the pumps for one reason or another proved inadequate for their task.
Mr Glidewell for the respondent did not seek in this House to contend that the justices' conclusion involved a finding of negligence and to support the conviction on that ground. On the evidence given, it is apparent that the justices might well have concluded that there was negligence in not appreciating by 3.45 pm that the pumps were not working properly, and, in view of the improbability that sufficient debris to block the impellers and the vents of both pumps had been sucked in in the course of the Monday and Tuesday, that there had been negligence in the inspection at the weekend.
In view of the attitude taken by the respondent, although it may be that the justices were in fact of the opinion that there had been negligence, one must treat this case as one in which there was no finding of negligence on the part of the appellants.
In the Divisional Court, Lord Parker CJ and Widgery LJ were infavour of dismissing the appeal. They found it unnecessary to consider whether the offence charged was an absolute offence. They were satisfied that the actions of the appellants were a cause of the pollution and that in their opinion sufficed. Bridge J, dissenting, held that there could be no criminal liability for causing polluting matter to enter a stream unless there was actual knowledge on the part of the alleged offender or at least the means of knowledge that his act might be expected to lead to pollution.
In this House Mr Drake for the appellants again contended that the appellants had not caused the pollution; that the section did not create an absolute offence and that the appellants could not be convicted in the absence of knowledge or negligence on their part. He also contended that in a section which, like s 2(1), creates two offences, the fact that knowledge is required for one leads to the presumption that it is also required for the other, in other words, that s 2(1)(a) should be read as if it said 'if he knowingly causes or knowingly permits'. He also relied on the well known principle that if the wording of a penal statute is capable of two interpretations, that most favourable to the accused should be taken as the correct interpretation.
The first question I propose to consider is, leaving the question of mens rea on one side, whether on the evidence the act or acts of the appellants caused the pollution. Its immediate cause was the blocking of the impellers and vents.
The presence of the polluting liquid on the bank of the river, and it would appear, within a foot or so of the river, was due to the facts of the appellants. The provision of the the river was directly due to their acts. When the works were operating, there was, under the system which they had instituted, bound to be an overflow into the river unless the pumps provided were of sufficient capacity and working sufficiently efficiently to prevent that happening.
If they had not installed any pumps or only pumps of insufficient capacity and an overflow into the river had followed from the operation of the works I do not think it could be suggested that their acts had not caused the overflow and consequent pollution. Does it make any difference if they had installed pumps of sufficient capacity and for some reason the pumps had broken down or were only able to pump a fraction of what they should have? I think not. It was the operation of the works which led to the flow of liquid to the tanks. It was that operation which, with the system they had installed, led to the liquid getting into the river. The roses at the end of the intake pipes must have been fitted because it was realised that there was a risk that without them debris would be sucked into and block the pumps. The fact that despite them debris was sucked in and prevented the pumps from working properly shows that that safeguard was insufficient and the result was the same as that which would have followed from the operation of the works if pumps of insufficient capacity had originally been installed.
In these circumstances I see no escape from the conclusion that it was the facts of the appellants that caused the pollution. Without their acts there would not have been this pollution. It was their operation of their works that led to the liquid getting into the tanks and their failure to ensure that the pumps were working properly that led to the liquid getting into the river. I therefore think that the justices' conclusion on the facts was right.
Then it is said that even if that was so, there should not have been a conviction for the offence charged was not an absolute offence. As my noble and learned friend, Lord Diplock, said in Sweet v Parsley  AC 132 , 162:
'The expression "absolute offence"... is an imprecise phrase currently used to describe an act for which the doer is subject to criminal sanctions, even though when he did it he had no mens rea; but mens rea itself also lacks precision...'
In this case it was argued that it was an essential ingredient of the offence that the appellants should -- the case being dealt with as if there was no negligence -- have intended the entry of the polluting matter into the river, that is to say, that they should have intended the commission of the offence. I cannot think that that was the intention of Parliament for it would mean that a burden of proof would rest on the prosecution that could seldom be discharged. Only if the accused had been seen tipping the polluting material into a stream or turning on a tap allowing a polluting liquid to flow into a stream or doing something of a similar character could the burden be discharged. Parliament cannot have intended the offence to be of so limited a character. Ordinarily all that a river authority can establish is that a discharge has come into a stream from a particular source and that it is of a polluting character. But the Act does not say that proof of that will suffice. If that were so, the Act would indeed create an absolute offence. It has also to be proved that the accused caused or knowingly permitted the pollution.
This Act is, in my opinion, one of those Acts to which my noble and learned friends, Lord Reid and Lord Diplock, referred in Sweet v Parsley  AC 132, 149, 163 which, to apply the words of Wright J in Sherras v De Rutzen  1 QB 918, 922, deals with acts which 'are not criminal in any real sense, but are acts which in the public interest are prohibited under a penalty'.
What, then, is meant by the word 'caused' in the subsection? If a man intending to secure a particular result, does an act which brings that about, he causes that result. If he deliberately and intentionally does certain acts of which the natural consequence is that certain results ensue, may he not also be said to have caused those results even though theymay not have been intended by him? I think he can, just as he can be said to cause the result if he is negligent, without intending that result.
I find support for my view in the observations of Bowen LJ in Kirkheaton District Local Board v Ainley, Sons & Co  2 QB 274. He said, at p 283:
'It appears to me that any person causes the flow of sewage into a stream... who intentionally does that which is calculated according to the ordinary course of things and the laws of nature to produce such flow.'
We have not here to consider what the position would be if pollution was caused by an inadvertent and unintentional act without negligence. In such a case it might be said that the doer of the act had not caused the pollution although the act had caused it. Here the acts done by the appellants were intentional. They were acts calculated to lead to the river being polluted if the acts done by the appellants, the installation and operation of the pumps, were ineffective to prevent it. Where a person intentionally does certain things which produce a certain result, then it can truly be said that he has caused that result, and here in my opinion the acts done intentionally by the appellants caused the pollution.
I now turn to the contention that the subsection should be read as if the word 'knowingly' appeared before 'causes'. Whether the inclusion of that word before 'permits' makes any difference to the meaning of 'permits', is, I think, open to doubt, for as Lord Goddard CJ said in Lomas v Peek 1947] 2 All ER 574, 575:
'If a man permits a thing to be done, it means that he gives permission for it to be done, and if a man gives permission for a thing to be done, he knows what is to be done or is being done...'
(See also per Lord Diplock in Sweet v Parsley  AC 132, 162.)
If the insertion of 'knowingly' before 'causes' meant only that the acts which produced the result must be intentional, then that insertion would not, in my view, add anything to the meaning to be given to the subsection. If, on the other hand, it meant that the accused must know what the end result would be, then it imports the requirement of a guilty mind accompanying the acts.
In this connection reliance was placed on Derbyshire v Houliston  1 QB 772. That was a decision on a very different statute and I do not think that it constitutes any authority for the proposition that in this Act s 2(1)(a) must be read as if the word 'knowingly' appeared before 'causes'. I therefore reject this contention.
In support of the contention that the offence in question is an absolute one, the appellants relied on the last part of s 2(1) which provides that a local authority shall be deemed to cause or knowingly permit pollution which passes into a stream from a sewer or sewage disposal works of theirs where the local authority were bound to receive the polluting matter into the sewer or sewage disposal unit or had consented to do so. This was obviously intended to deal with a special case and to prevent a local authority from being able to contend that in such circumstances they had not caused the pollution. I do not consider that it throws any light on the meaning to be given to s 2(1)(a).
The function of the courts is to interpretan act 'according to the intent of them that made it': Coke, 4 Institutes (1817), p 330. If the language of a penal statute is capable of two interpretations, then that most favourable to the subject is to be applied. Having regard to the nature of the Rivers (Prevention of Pollution) Act 1951, the mischief with which it was intended to deal and the fact that it comes within the category of acts to which my noble and learned friends, Lord Reid and Lord Diplock, referred in Sweet v Parsley  AC 132. I do not think that the subsection is capable of two interpretations or that it was intended to be interpreted or should be interpreted as making the causing of pollution only an offence if the accused intended to pollute.
For these reasons I would dismiss the appeal with costs.
LORD PEARSON: My Lords, the appellants have their Mount Sion Works at Radcliffe beside the River Irwell in Lancashire. Water is drawn from the river along a goit and is taken into the works and used in procession manilla fibres for use in papermaking. The first stage of the processing produces a very strong effluent which is removed by tankers and disposed of elsewhere; no question arises with regard to that effluent. At the second stage of the processing the fibres are washed, and this leaves polluted washing water, which is taken down to two settling tanks on the banks of the river. After some purification by settling, this water is recirculated and used again in the processing. There are two pumps which draw water out of the settling tanks; one of these operates automatically in the sense that it switches itself on whenever the water in one of the settling tanks has risen to a certain level; the other is a standby pump which can be switched on manually when the automatic pump is not keeping down the level of the water. At the bottom of the intake pipe of each pump there is a rose, similar in principle to the rose in a watering can, with holes of 3/4 inch diameter, intended to keep out foreign matter while admitting a sufficient inflow of water. As the settling tanks are beside the river, it must follow that, if the pumps fail to keep down the level of the water and the rising water overflows, the overflow must be into the river, and it is polluted water.
On 25th November 1969 the processing plant had been in use for about a year, and it was being operated on that day. The foreman inspected the tanks at 8.15 am, and found the automatic pump working and everything normal. When he inspected the tanks again at 11.30 am he found that the water level had risen and he switched on the standby pump. At 1.15 pm, and again at 3.45 pm, he found the water level unchanged with both pumps working. But at 4.30 pm, the river authority inspector visited the tanks and found that there was an overflow of polluted water from them into the river at a rate which he estimated at 250 gallons per hour. The inspector took a sample of the polluted water immediately before it entered the river and on analysis it was found that the biochemical oxygen demand on this sample was 160 milligrammes per litre whereas, when the river authority allowed a discharge of effluent, the biochemical oxygen demand should be no more than 20 milligrammes per litre.
What had happened was that in each of the pumps the impeller had become clogged with foreign matter -- brambles, bracken or ferns and long leaves -- which had entered the intake pipe through the holes in the rose.
There was evidence, accepted by the justices, from the appellants' fitter to the effect that he had inspected the rose and the impeller and emptied the rose once a week and had done so on the Sunday preceding 25th November 1969, which was a Tuesday; and that the rose had never been blocked before or since that date; but on that date he had found brambles, ferns and long leaves wrapped around the impeller and the vents blocked; he had never found such things before in the pumps.
There was also expert evidence, accepted by the justices, that the appellants had taken all reasonable steps to make sure water did not escape into the river. The expert witness did say, however, that an alarm system would be desirable but there was not one on 25th November 1969. The appellants' general manager said that as an extra aid to their foreman an alarm system, a probe actuating a bell, was installed in December 1969, but that this alarm system was not essential as two pumps were adequate to keep the effluent out of the River Irwell and one pump was normally more than adequate. The general manager also said that neither he nor anyone in authority had knowledge of the discharge of effluent until informed by the inspector. The foreman gave evidence of his regular inspection of the tanks. He said that the level of the water in the tanks depended on the amount of processing going on.
The justices said in the case stated:
'We were of the opinion that the Appellants had caused the polluting matter to enter the River by their failure to ensure that the apparatus was maintained in a satisfactory condition to do the job for which it was provided. We accordingly convicted the Appellants.'
Counsel have stated that the Divisional Court with the assent of counsel assumed that the justices had not made any finding of negligence. Although perhaps a different view might have been taken of the evidence, I think, having regard to the findings of fact, that the assumption has to be made.
The relevant enactment is s 2(1)(a) of the Rivers (Prevention of Pollution) Act 1951, providing that:
'Subject to this Act, a person commits an offence punishable under this section -- (a) if he causes or knowingly permits to enter a stream any poisonous, noxious or polluting matter...'
The question is whether the justices could properly find that the appellants caused the polluted water to enter the River Irwell.
It has been contended that the prosecution had to prove mens rea on the part of the appellants, and consequently the appellants were wrongly convicted because, even if they caused the polluted water to enter the river, they did not do so intentionally or knowingly. In my opinion, this contention fails. First, in the wording of the enactment there is the contrast between 'causes' and 'knowingly permits', raising the inference that knowledge is not a necessary ingredient in the offence of 'causing'. Secondly, mens rea is generally not a necessary ingredient in an offence of this kind, which is in the nature of a public nuisance. In Sherras v De Rutzen  1 QB 918 Wright J said, at pp 921-922:
'There is a presumption that mens rea, an evil intention, or a knowledge of the wrongfulness of the act, is an essential ingredient in every offence; but that presumption is liable to be displaced either by the words of the statute creating the offence or by the subject-matter with which it deals, and both must be considered: Nichols v. Hall (1873) LR 8 CP 322... the principal classes of exceptions may perhaps be reduced to three... Another class comprehends some, and perhaps all, public nuisances: Reg. v. Stephens (1866) LR 1 QB 702 where the employer was held liable on indictment for a nuisance caused by workmen without his knowledge and contrary to his orders; and so in Rex v. Medley (1834) 6 C &P 292 and Barnes v. Akroyd (1872) LR 7 QB 474.'
In R v Medley 6 C &P 292 there was an indictment against the directors and other officers of a gas company for discharging the refuse of gas manufacture into the Thames. Denman CJ in summing up said to the jury, at p 299:
'It is said that the directors were ignorant of what had been done. In my judgment that makes no difference; provided you think that they gave authority to Leadbeter to conduct the works, they will be answerable.'
There is an authority on a similar enactment. In Moses v Midland Railway Co 113 LT 451 the railway company were conveying on their line a private owner's tank wagon containing creosote, and on the journey the creosote began to leak out from a defective tap and when this was discovered the train was stopped and the defect was remedied. Some of the creosote which leaked out found its way into a tributary of a salmon river. The railway company were prosecuted under s 5 of the Salmon Fishery Act 1861, where the relevant wording was:
'Every person who causes or knowingly permits to flow, or puts or knowingly permits to be put, into any waters containing salmon, or into any tributaries thereof, any liquid or solid matter to such an extent as to cause waters to poison or kill fish, shall incur the following penalties;...'
Lord Reading CJ dealt only with causation. Avory J dealt with mens rea at the beginning of his judgment, where he said, at p 453:
'I have had some doubt about this case, because when it was first read to us I certainly understood it to mean that the creosote which caused the damage in fact escaped from this tank while the train was pulled up and while the operations were going on for the purpose of repairing it. If that had been clearly the state of facts I should have hesitated before agreeing with the view that under these circumstances the railway company were not causing the liquid to flow into the stream within the meaning of this section, because it appears to me to be not one of those cases where it is necessary to prove any mens rea. It is an absolute prohibition, and the person liable is the person who in fact causes the liquid to flow; and I do not think it is necessary to shew in the words of one of the judgments quoted to us, that the person was intentionally causing the liquid to flow.'
I think the judgments of Lord Esher MR and Bowen LJ in Kirkheaton District Local Board v Ainley, Sons & Co  2 QB 274, 281, 283 tend to show that mens rea was not a necessary ingredient in the offence of causing sewage to fall or flow into a stream contrary to the Rivers Pollution Prevention Act 1876. Lord Esher MR said, at p 281:
'The sewage matter starts from their premises by their volition in such a way that it must go through a sewer, which, by the natural process of gravitation, will carry it into the stream. Reading the words of the Act according to their ordinary meaning, did or did not the defendants cause the sewage, which they thus sent from their premises, to flow into the stream? It seems to me that they did. Unless they had done what they did, it would not have flowed into the stream. They seem to me to be the causa causans, or, at any rate, the causa sine qua non.'
The view that mens rea is not a necessary ingredient in an offence of this kind seems to me to be consistent with, and supported by, what was said in Sweet v Parsley  AC 132 by Lord Pearce at p 156 and by Lord Diplock at p 163.
The appellants' other contention is that they did not cause the polluted water to flow into the river. I think that their main grounds for this contention are that they did not intend the polluted water to flow into the river, they did not know it was happening and (according to the assumption that has been made) it did not happen by reason of any negligence on their part.
On the general question of causation there is an illuminating passage in the speech of Lord Shaw of Dunfermline in Leyland Shipping Co v Norwich Union Fire Insurance Society  AC 350. He said, at p 369:
'To treat proxima causa as the cause which is nearest in time is out of the question. Causes are spoken of as if they were as distinct from one another as beads in a row or links in a chaim, but -- if this metaphysical topic has to be referred to -- it is not wholly so. The chain of causation is a handy expression, but the figure is inadequate. Causation is not a chain, but a net. At each point influences, forces, events, precedent and simultaneous, meet; and the radiation from each point extends infinitely. At the point where these various influences meet it is for the judgment as upon a matter of fact to declare which of the causes thus joined at the point of effect was the proximate and which was the remote cause.'
This passage may have been partly inspired by the argument of R A Wright KC, at pp 352-353. In Yorkshire Dale Steamship Co Ltd v Minister of War Transport, The Coxwold  AC 691, Viscount Simon LC said, at p 698:
'The interpretation to be applied does not involve any metaphysical or scientific view of causation. Most results are brought about by a combination of causes, and a search for "the cause" involves a selection of the governing explanation in each case'.
Lord Wright said, at p 706:
'This choice of the real or efficient cause from out of the whole complex of the facts must be made by applying commonsense standards.'
In Cork v Kirby Maclean Ltd 1952] 2 All ER 402, Denning LJ said, at p 407:
'It is always a matter of seeing whether the particular event was sufficiently powerful a factor in bringing about the result as to be properly regarded by the law as a cause of it...'
When one sets out to select in this case from the whole 'complex of the facts' the 'governing explanation' of the overflow of polluted water into the river there are a number of factors to be taken into account. These include the absence of intention, the absence of knowledge and the assumed absence of negligence on the part of the appellants. It would have been easier to decide that they caused the overflow if they had intended it or known of it when it was happening or brought it about by their negligence.
Nevertheless, I think that the justices and the majority of the Divisional Court were right in holding that the overflow was caused by the activities of the appellants. Those were positive activities and they directly brought about the overflow. What other cause was there? There was no intervening act of a trespasser and no act of God. There was not even any unusual weather or freak of nature. Autumn is the season of the year in which dead leaves, ferns, pieces of bracken and pieces of brambles may be expected to fall into water and sink below the surface and, if there is a pump, to be sucked up by it.
In my opinion, the activities of the appellants were the cause of the overflow of polluted water into the river. It is not necessary for the purposes of this case to decide whether a conviction should be upheld if the activities of a defendant were to be regarded as only a cause of such an overflow. Subject to reservation of that question I agree with the judgments of the majority in the Divisional Court.
I would dismiss the appeal.
LORD CROSS OF CHELSEA: My Lords, I have found this a difficult case. At one time I was inclined to agree with the dissenting judgment of Bridge J  1 QB 127, 136-138; but in the end I have come to the conclusion that the appeal should be dismissed.
The appellants in the course of their business cause large quantities of polluted effuent to flow into a settling tank on the bank of the River Irwell. The tank would have inevitably overflowed with the result that the effluent would have entered the river had not the appellants installed two pumps to keep the level of the water in the tanks low enough to prevent any overflow. At the base of the pumps there are or were metal 'roses' with holes of a diameter of 3/4 inch designed to allow water to reach the pump freely but to prevent any solid matter which might get into the tank from passing through the rose and coming into contact with the impeller.
On Tuesday, 25th November 1969, the pumps failed to prevent the settling tank from overflowing, the reason for the failure being -- as was subsequently discovered -- that a quantity of brambles, leaves and other vegetable matter had found its way through the holes in the 'roses' and was wound round theimpellers. The evidence, which the justices accepted, was to the effect that the 'roses' had been regularly inspected each weekend since they had been installed a year previously, that no vegetable matter had been in them when the pumps were inspected a few days before the overflow, and indeed that no vegetable matter had ever been found in the pumps before. How all these brambles and leaves had found their way through the roses in the course of the two or three days before 25th November was an unsolved mystery.
These being the facts, did the appellants commit the offence created by s 2 of the Rivers (Prevention of Pollution) Act 1951 of 'causing' the polluted effluent to enter the river? Bridge J said  1 QB 127, 136 -- and I agree with him -- that the contrast drawn in the section between 'causing' and 'knowingly permitting' shows that a man cannot be guilty of causing polluting matter to enter a stream unless at the least he does some postive act in the chain of acts and events leading to that result. I cannot, however, follow him when he goes on to say that it is also necessary if the man is to be held to have 'caused' the result that he should have known or have had the means of knowledge that his act might be expected to lead to it. Suppose that the contractor whom the appellants had employed to install these works on the bank of the Irwell had provided a defective pump with the result that when the appellants operated their plant for the first time the tank had overflowed -- surely they could fairly be said to have 'caused' the pollution of the river even though they neither knew nor had any means of knowing that their act in setting the plant in operation would lead to that result? But, of course, the appellants can say -- and here lies the strength of their case-- that the justices have not found that the pumps, albeit they had such wide holes in the roses, were unsuitable and that they have accepted the evidence of their employees as to the frequency and thoroughness of their inspections. This enables them to advance the argument which was accepted by Bridge J  1 QB 127, 137 that the unexplained presence of this quantity of vegetable matter wrapped round the impellers should be regarded as a separate cause of the pollution of the stream which relieves the appellants from the responsibility for it. 'If it had been shown that the brambles had been put there by a trespasser' so the argument runs 'the appellants could not be held to have "caused" the overflow. For all that one knows they may have been put there by a trespasser. What difference does it make that one cannot say how they came there providing that the appellants have not been shown to be in anyway to blame for their presence?' This argument is plausible -- but I think fallacious. The appellants did not advance any evidence to show that the brambles had been placed there by a trespasser or that the 'inanimate forces' -- to use the words of Bridge J, at p 137 -- which brought them there were in the category of acts of God -- analogous to the destruction of the pumps by lightning or the flooding of the tank by a storm of altogether unexampled severity and duration. All that the evidence shows is that despite the false sense of security into which the appellants had been lulled by their experience over the past 12 months, vegetable matter was in fact liable to collect quite quickly inside the roses and that, although it may not be fair to blame them for not inspecting the roses more often than once a week, if they did not have more frequent inspections they were running the risk of 'causing' polluting effluent to enter the river. It was not for the respondent to prove that the appellants had been negligent. The appellants having started to operate their plant on that day could only escape being held to have caused polluted effluent to enter the river if they proved that the overflow of the tank had been brought about by some other event which could fairly be regarded as being beyond their ability to foresee or control.
I would, therefore, dismiss the appeal.
LORD SALMON: My Lords, I agree that this appeal should be dismissed and I wish to add only a few brief observations of my own. It is undisputed that the river on the banks of which stand the appellants' Mount Sion Works was polluted by contaminated effluent which flowed from those works into the river. The vital question is whether the appellants caused that pollution within the meaning of s 2(1) of the Rivers (Prevention of Pollution) Act 1951. The nature of causation has been discussed by many eminent philosophers and also by a number of learned judges in the past. I consider, however, that what or who has caused a certain event to occur is essentially a practical question of fact which can best be answered by ordinary common sense rather than abstract metaphysical theory.
It seems to me that, giving the word 'cause' its ordinary and natural meaning, anyone may cause something to happen, intentionally or negligently or inadvertently without negligence and without intention. For example, a man may deliberately smash a porcelain vase; he may handle it so negligently that he drops and smashes it; or he may without negligence slip or stumble against it and smash it. In each of these examples, no less in the last than in the other two, he has caused the destruction of the vase.
The appellants clearly did not cause the pollution intentionally and we must assume that they did not do so negligently. Nevertheless, the facts, so fully and clearly stated by my noble and learned friend, Viscount Dilhorne, to my mind make it obvious that the appellants in fact caused the pollution. If they did not cause it, what did? There was no intervening act of a third party nor was there any act of God to which it could be attributed. The appellants had been responsible for the design of the plaint; everything within their works was under their control; they had chosen all the equipment. The process which they operated required contaminated effluent being pumped round their works until it came to rest in an open tank which they sited on the river bank. If the pumps which they had installed in this tank failed to operate efficiently the effluent would necessarily overflow into the river. And that is what occurred. It seems plain to me that the appellants caused the pollution by the active operation of their plaint. They certainly did not intend to cause pollution but they intended to do the acts which caused it. What they did was something different in kind from the passive storing of effluent which could not discharge into the river save by an act of God or, as in Impress (Worcester) Ltd v Rees  2 All ER 357, by the active intervention of a stranger, the risk of which could not reasonably have been foreseen.
The appellants relied strongly on Moses v Midland Railway Co 31 TLR 440. In that case a private owner's tank wagon filled with creosote formed part of a train being driven by the defendants. At the beginning of the journey the wagon was subjected to careful examination by the defendants which revealed no defect. There was, however, a latent defect in one of its taps. Whilst the train was travelling along the banks of a river this defect caused creosote to leak into the river and polluted it so that many fish were killed. On a charge under s 5 of the Salom Fishery Act 1861 the justices held that the defendants had not caused the pollution, and that decision was upheld by the Divisional Court. The facts were strikingly different from those of the present case. The wagon was not owned by the defendants, they were in no way responsible for its design or maintenance; they exercised no control over the defective tap; and they had no knowledge or means of knowledge of the latent defect which caused the leak. The decision, which to my mind is not relevant to this appeal, may well have been correct on its facts although the judgments as reported are not very satisfactory.
The appellants contend that even if they caused the pollution still they should succeed since they did not cause it intentionally or knowingly or negligently. Section 2(1)(a) of the Rivers (Prevention of Pollution) Act 1951 is undoubtedly a penal section. It follows that if it is capable of two or more meanings then the meaning most favourable to the subject should be adopted. Accordingly, so the argument runs, the words 'intentionally' or 'knowingly' or 'negligently' should be read into the section immediately before the word 'causes'. I do not agree. It is of the utmost public importance that our rivers should not be polluted. The risk of pollution, particularly from the vast and increasing number of riparian industries, is very great. The offences created by the 1951 Act seem to me to be prototypes of offences which 'are not criminal in any real sense, but are acts which in the public interest are prohibited under a penalty': Sherras v De Rutzen  1 QB, per Wright J at p 922, referred to with approval by my noble and learned friends, Lord Reid and Lord Diplock in Sweet v Parsley  AC 132, 149, 162. I can see no valid reason for reading the word 'intentionally', 'knowingly' or 'negligently' into s 2(1)(a) and a number of cogent reasons for not doing so. In the case of a minor pollution such as the present, when the justices find that there is no wrongful intention or negligence on the part of the defendant, a comparatively nominal fine will no doubt be imposed. This may be regarded as a not unfair hazard of carrying on a business which may eause pollution on the banks of a river. The present appellants were fined £20 and ordered to pay in all £24 costs. I should be surprised if the costs of pursuing this appeal to this House were incurred to the purpose of saving these appellants £44.
If this appeal succeeded and it were held to be the law that no conviction could be obtained under the 1951 Act unless the prosecution could discharge the often impossible on us of proving that the pollution was caused intentionally or negligently, a great deal of pollution would go unpunished and undeterred to the relief of many riparian factory owners. As a result, many rivers which are now filthy would become filthier still and many rivers which are now clean would lose their cleanliness. The legislature no doubt recongised that as a matter of public policy this would be most unfortunate. Hence s 2(1)(a) which encourages riparian factory owners not only to take reasonable steps to prevent pollution but to do everthing possible to ensure that they do not cause it.
I do not consider that the appellants can derive any comfort (as they seek to do) from the inclusion in s 2(1)(a) of the words 'knowingly permits' nor from the deeming provision against local authorities in relation to sewage escaping into a river from sewers or sewage disposal units. The creation of an offence in relation to permitting pollution was probably included in the section so as to deal with the type of case in which a man knows that contaminated effluent is escaping over his land into a river and does nothing at all to prevent it. The inclusion of the word 'knowingly' before 'permits' is probably otiose and, if anything,is against the appellants, since it contrasts with the omission of the word 'knowingly' before the word 'causes'. The deeming provision was probably included to meet what local authorities might otherwise have argued was a special case and cannot, in my opinion, affect the plain and unambiguous general meaning of the word 'causes'.
For these reasons I would dismiss the appeal with costs.
Appeal dismissed with costs.
Beardall, Fenton & Co, agents for Elliott & Buckley, Manchester (for the appellants)
Norton, Rose, Botterell & Roche, agents for R E Woodward, Warrington (for the respondent)