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Cite as: [2000] PIQR Q293, [2000] ICR 1086, [2000] 3 ALL ER 421, [2000] EWCA Civ 111, [2000] Lloyd's Rep Med 254

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JISCBAILII_CASE_TORT

Case No: QBENF 1999/1045/A2

IN THE SUPREME COURT OF JUDICATURE
COURT OF APPEAL (CIVIL DIVISION)
ON APPEAL FROM QBD (HH Judge Altman
sitting as a High Court Judge)
Royal Courts of Justice
Strand, London, WC2A 2LL
Thursday 6 April 2000
B e f o r e :
LORD JUSTICE STUART-SMITH
LORD JUSTICE MUMMERY
and
LORD JUSTICE CLARKE

	HOLTBY	Appellant
	- and -
	BRIGHAM & COWAN (HULL) LTD	Respondent

_____________________________
(Transcript of the Handed Down Judgment of
Smith Bernal Reporting Limited, 180 Fleet Street
London EC4A 2HD
Tel No: 0171 421 4040, Fax No: 0171 831 8838
Official Shorthand Writers to the Court)
_____________________________
Kieron May (instructed by Messrs Philip Hamer for the Appellant)
Anthony Goldstaub QC & Richard Seabrook (instructed by Messrs Whitfield Hallam Goodallfor the Respondent)
_____________________________
Judgment
As Approved by the Court
Crown Copyright ©

LORD JUSTICE STUART-SMITH:
The question in issue
1. This case raises a point of general importance which, surprisingly, does not appear to have been considered previously by this court. The question is this: where a claimant suffers injury, in this case asbestosis, as a result of exposure to a noxious substance by two or more persons, is the defendant who is one of those persons whose tortious act has made a material contribution to the injury, liable in respect of the whole resulting disability, subject only to such rights as he only has against other tortfeasors? Or, is he liable only to the extent that he has contributed toward the disability? HH Judge Altman, sitting as a High Court Judge, in a conspicuously careful and succinct judgment, which dealt with many other aspects of the case including liability, limitation and the effect on the overall disability of such matters as smoking, obesity and arthritis unconnected with the tortious conduct, held that the latter was the correct answer. The claimant now appeals.
The facts
2. Mt Holtby, the claimant, was born on 7 July 1927. For much of his working life he worked from 1942 to 1981 as a marine fitter. In this work he was exposed to asbestos dust. For about half this time, namely some 12 years, he was employed by the defendants; for the remainder he was employed by other employers doing similar work in similar conditions; in some cases for quite long periods, such as 5, 4, 2 and 1½ years overall; in other cases for periods measured in months.
The Judge's conclusion
3. The judge held that the defendants were negligent and in breach of statutory duty and the claim was not statute barred. On the question of the extent of the defendant's responsibility he said:
"The evidence is clear, namely that the degree of exposure to asbestos dust makes a difference to the degree to which a particular patient will suffer the disease. Quantification is, however, difficult. Different people respond differently to the inhalation of asbestos, and they respond at different rates at different points of time. Whilst there is a cumulative effect recognised by both specialists, the mere fact that half his working life was with the Defendants cannot do anything other than produce a reason for taking that factor into account. Any mathematical approach is clearly unsupportable on the evidence. In the end my assessment is based on the way this matter was put by Dr Page:
"It is cumulative exposure which causes the asbestos and aggravates it......if the Plaintiff had sustained exposure to asbestos dust only whilst working for the Defendants his condition would probably be less."
The Defendants are liable only for that damage which they have caused, but the quantification of that factor is difficult. Whilst there is no mathematical division to be made in medical terms, for the purpose of assessment I have felt bound to apply a discount factor and I have done so in the amount of 25%."
4. He assessed the general damages in respect of the disability caused by the asbestosis at £32,000, which he reduced by 25% to £24,000. He then considered several items of special damage and future loss such as inability to do DIY jobs, additional transport costs, care and attendance and extra heating which he assessed globally at £15,000 and reduced by 25% to £11,250. In respect of loss of pension, he held that the claimant's expectation of life was shortened by two years and he assessed the loss at £800. He made no deduction in respect of this. Mr Goldstaub QC, who appeared on behalf of the respondents, submitted that as a matter of strict logic the judge should have made a similar deduction; but there is no cross-appeal on this point.
The appellant's submissions
5. Mr May, who appeared on behalf of the appellant, made two main submissions:
(1) That as a matter of procedure the judge ought not to have made any deduction; and
(2) That as a matter of principle on the evidence available, the judge should not have made a deduction.
The procedural point
6. Mr May submits that the defendants should have pleaded the point that they were not responsible for all the claimant's disability but only a proportion of it having regard to similar exposure elsewhere. He submits that the onus of proving this rests on the defendants; further, that even if it did not, the defendants should have pleaded it because it was a `fact on which the defendants relied in mitigation of, or otherwise in relation to, the amount of damages' within RSC Order 18 r.12. The defendant's pleading merely stated that `causation is denied'. And further and better particulars were no more illuminating.
7. The question was apparently raised on the first day of the trial. It seems that there was a misunderstanding between the judge, and Mr May says himself, on the one hand, and Mr Seabrook on the other, as to whether this was going to be an issue in the case. Mr Seabrook intended that it should be; the judge understood that it was not. The matter was not put in cross-examination specifically by Dr Howard, the claimant's expert; but the matter was raised again in the course of the evidence by Dr Page, the defendant's expert. At Transcript p2C:
" Q. No, and it may follow already from the answer that you have given, but the longer one is in an environment with asbestos dust. How does that impinge on......
A. Oh, yes. I mean, all exposures to asbestos contribute to the development of asbestosis. It is cumulative exposure that causes it and they are all relevant.
Q. Yes. Putting it another way......
Q. Judge Altman: It causes it but it also aggravates it as well?
A. Yes, yes, ....."
Dr Page then points out that only about half the exposure lies with the defendant. At G he is asked:
" Q. However, if we were dealing simply with the period of exposure at Brigham and Cowan and there had not been that other exposure, what would you have expected in terms of the level of asbestosis that this individual was suffering from?
A. Well, I think it would be less than it is now but, I mean, I would not suggest that 12 years exposure to asbestos is unlikely to have caused asbestosis. I think that...
Q. No.
A. .....He would still have it, but probably less."
At this point Mr May intervened and there was discussion as to the significance of the evidence, in particular whether it amounted to a defence or was relevant to the issue of causation. There was also discussion of what Dr Howard had said on the subject. This exchange followed at p6B:
" Judge Altman: But he [Dr Howard] did say it was cumulative.
Mr Seabrook: My Lord, that is certainly my recollection, which was sufficient....
Judge Altman: The exposure, he said, would contribute to asbestosis even though there were the same exposure elsewhere.
Mr Seabrook: Yes.
Judge Altman: That is my note of his evidence, which I think is basically what Dr Page has just said."
8. Mr May did not insist that the matter should be pleaded and as appears from his judgment the judge did not think that strictly speaking it needed to be. Mr May did not seek an adjournment or ask to recall Dr Howard. Moreover, it was the judge's view, with which I concur, that to anyone experienced in this type of case, and there are few who were more so than Mr May and his solicitors, that it was apparent from Dr Page's report and covering letter (a copy of which was sent to the claimant's solicitors) that this was an issue. The last paragraph of the letter was in these terms:
"It is also clear that Mr Holtby had significant exposure to asbestos with employers other than Brigham and Cowan (Hull) Ltd and I have made reference to this in the body of my report."
9. Dr Page took a careful history from the appellant and set out details of his employments. At p57 of the Core Bundle he said:
"All periods in which Mr Holtby was exposed to asbestos should be considered relevant in causing the pleural disease and mild asbestosis."
10. The point was fully argued in final submissions. In my judgment the judge was in the best position to decide whether the issue had been properly raised and considered. I am not impressed with Mr May's argument that he would have wanted to ask Dr Howard further matters about it. I shall have to refer to some of Mr May's own cross-examination of Dr Page when I consider whether the evidence supported the judge's conclusion. In any event I do not think this court should interfere with the judge's decision on the procedural aspect of the case.
The point of principle
11. Mr May submits that all the claimant has to prove is that if the defendant's conduct made a material contribution to his disease he is entitled to recover all his loss from that defendant, notwithstanding that others may have contributed as well. The defendant is then left to his remedy against other tortfeasors. Alternatively, he submits that once the claimant has proved that the defendant's conduct made a material contribution to his disease, the onus is upon the defendant to plead and prove that others were responsible for some and, if so, what part of the injury.
12. In support of his first proposition Mr May relies on the case of Bonnington Castings & Wardlow [1956] AC 613. In that case the pursuer, who was employed by the defendants, was exposed to two sources of silica dust which together caused him to contract pneumoconiosis. The first source was from the pneumatic hammer at which he worked. There was no known or practicable method of removing that dust. The other was from swing grinders in respect of which the defendants failed negligently and in breach of statutory duty to provide adequate protection. The Lord Ordinary and the majority of the First Division of the Court of Session held that the onus was on the defendants to show that the dust from the swing grinders did not cause the pursuer's disease.
13. The House of Lords rejected this approach. They held that the onus of proving causation was on the pursuer, but it was sufficient for him to succeed, to show that the guilty dust, that is from the swing grinders, caused or materially contributed to the disease. Lord Reid at p620A said:
"It would seem obvious in principle that a pursuer or plaintiff must prove not only negligence or breach of duty but also that such fault caused or materially contributed to his injury, and there is ample authority for that proposition both in Scotland and in England. I can find neither reason nor authority for the rule being different where there is breach of statutory duty. The fact that Parliament imposes a duty for the protection of employees has been held to entitle an employee to sue if he is injured as a result of a breach of that duty, but it would be going a great deal farther to hold that it can be inferred from the enactment of a duty that Parliament intended that any employee suffering injury can sue his employer merely because there was a breach of duty and it is shown to be possible that his injury may have been caused by it. In my judgment, the employee must in all cases prove his case by the ordinary standard of proof in civil actions: he must make it appear at least that on a balance of probabilities the breach of duty caused or materially contributed to his injury."
14. What the House of Lords did not consider in that case was the extent of the defendants' liability, because it was never argued that the defendants were only liable to the extent of the material contribution. But the case makes it quite clear that proof of causation is a matter for the claimant.
15. Bonnington's case was followed in McGhee v National Coal Board [1973] 1 WLR 1. The pursuer contracted dermatitis from contact with brick dust in the course of his employment. Proper provision of washing facilities would have ameliorated the position and the defendants were negligent in not providing them. But the pursuer would still have been exposed to some dust which could not be avoided. He could not prove however that provision of washing facilities would have prevented him contracting the disease. It was held that the absence of washing facilities materially increased the risk of injury and therefore the pursuer had proved that it made a material contribution to the disease.
At page 11G Lord Salmon said:
"I, of course, accept that the burden rests upon the pursuer to prove, on a balance of probabilities, a causal connection between his injury and the defenders' negligence. It is not necessary however, to prove that the defenders' negligence was the only cause of injury. A factor, by itself, may not be sufficient to cause injury but if, with other factors, it materially contributes to causing injury, it is clearly a cause of injury. Everything in the present case depends upon what constitutes a cause. I venture to repeat what I said in Alphacell Ltd v Woodward [1972] AC 824, 847:
"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."
In the circumstances of the present case it seems to me unrealistic and contrary to ordinary common sense to hold that the negligence which materially increased the risk of injury did not materially contribute to causing the injury."
Once again the question of the extent of the defendant's liability was not considered, since like the defendants in Bonnington's case their case was that they were not liable at all.
16. Of that case Lord Bridge of Harwich in Wilsher v Essex Health Authority [1988] AC 1074 at 1090C:
"The conclusion I draw from these passages is that McGhee v National Coal Board [1973] 1 WLR 1 laid down no new principle of law whatever. On the contrary, it affirmed the principle that the onus of proving causation lies on the pursuer or plaintiff, Adopting a robust and pragmatic approach to the undisputed primary facts of the case, the majority concluded that it was a legitimate inference of fact, that the defenders' negligence had materially contributed the pursuer's injury. The decision, in my opinion, is of no greater significance than that and to attempt to extract from it some esoteric principle which in some way modifies, as a matter of law, the nature of the burden of proof of causation which a plaintiff or pursuer must discharge once he has established a relevant breach of duty is a fruitless one."
17. In support of his alternative submission Mr May relied on two cases. The first is the case of Milner v Humphreys and Glasgow Ltd unreported transcript of 24.11.98, a decision of Longmore J. In that case the claimant had contracted asbestosis after an overall period of exposure of 4 years and 10 months with six different employers, only 7 months of which were with the defendants. Longmore J. said this:
"Many diseases depend on cumulative exposure: many disease may have more than one cause: some causes may be tortious in origin and some may be non-tortious. It may be difficult to separate the two. Where, as in Thompson v Smiths Shiprepairers [1984] QB 405, the operations of a single employer or the same operations of two consecutive employers may have been tortious only after a certain date justice may require and the facts may permit an apportionment to be made so that the tortious employer is not held liable for the consequences of non-tortious conduct of himself or [the conduct, tortious or otherwise of] another. Such cases do, however, present quite serious factual difficulties and the law has been concerned to ensure that a meritorious plaintiff does not fail for want of proof.
Mr May for the plaintiff submitted that where there are concurrent causes of industrial disease and a plaintiff can show that a defendant's breach of duty has materially contributed to the disease, he can recover for the consequences of that disease, see Bonnington Castings v Wardlaw [1956] AC 613. He then submitted that the same principle should apply to sequential causes of industrial disease.
I do not think that this argument can be accepted in the broad form in which it was put. As Mustill J. pointed out in Thompson at p441, the Bonnington principle is but a variant of the principle that, where an injury is indivisible, any tortfeasor whose act has been a proximate cause must compensate for the whole injury, leaving the tortfeasor to sort out with other possible tortfeasors any other appropriate claim for contribution, see Dingle v Associated Newspapers [1961] 2 QB 188 per Devlin LJ. Where there are causes concurrent in time, the likelihood is that a resulting injury will be indivisible; but where causes are sequential in time, it is not likely that an injury will be truly indivisible especially if (as I do not think Dr Howard contested) the injury is a disease which can get worse with cumulative exposure. Bonnington v Wardlaw can, nevertheless, assist the plaintiff to this extent; the principle, as formulated by Mustill J., is that where it is proved that a wrongful act has made a material contribution to the plaintiff's injury, the law regards this as sufficient discharge of the plaintiff's burden of proof on causation to render the defendant liable for the injury in full. That does not mean that no question of apportionment can ever arise but it does, in my judgment, mean that, unless the defendant pleads and proves facts which justify apportionment, the plaintiff can recover in full."
I have added the words in square brackets in the first paragraph to make the position complete.
18. The second case upon which Mr. May relies is Borel v. Fibreboard Paper Products Corp. and others 493F.2D (1973) a decision of the United States Court of Appeals Fifth Circuit. In the course of his working life the plaintiff's husband had been exposed to asbestos dust. He sued eleven of the manufacturers. He settled against four of them and a verdict was directed in favour of a fifth. The action continued against the remainder. The husband died and the action was carried on by his widow. The defendants contended that since the onus of proving causation was on the plaintiff and she could not establish which of the defendants had caused which if any damage, she must fail against all. This submission had apparently been accepted in the case of Sun Oil v. Robicheaux Tex.Civ. App 1930.23SW.2d 713. But it had been overruled in Lander v. East Texas Salt Water Dispersal Co. 151 Tex.251, 248 SW.2d 731. In Borel Wisdom J., giving the judgment of the court, summarised the effect of Lander's case in follows at p1095:
"Where several defendants are shown to have each caused some harm, the burden of proof (or burden of going forward) shifts to each defendant to show what portion of the harm he caused. If the defendants are unable to show any reasonable basis for division, they are jointly and severally liable for the total damages."
19. It seems to me with all respect that in the wholly understandable desire to avoid the totally unjust result of Robicheaux's case , in the last sentence of the passage cited the court has imposed very considerable injustice on the defendants amongst themselves, since ex hypothesi if they cannot prove anything against another, the defendant or defendants against whom the plaintiff chooses to execute, will be unable to recover any contribution from the others.
20. I do not accept Mr. May's submissions. In my judgment as the passages cited from the three House of Lords' decisions show, the onus of proving causation is on the claimant; it does not shift to the defendant. He will be entitled to succeed if he can prove that the defendants' tortious conduct made a material contribution to his disability. But strictly speaking the defendant is liable only to the extent of that contribution. However if the point is never raised or argued by the defendant, the claimant will succeed in full as in Bonnington and McGhee. I agree with Judge Altman that strictly speaking the defendant does not need to plead that others were responsible in part. But at the same time I certainly think it is desirable and preferable that this should be done. Certainly the matter must be raised and dealt with in evidence, otherwise the defendant is at risk that he will be held liable for everything. In reality I do not think that these cases should be determined on onus of proof. The question should be whether at the end of the day and on consideration of all the evidence, the claimant has proved that the defendant is responsible for the whole or a quantifiable part of his disability. The question of quantification may be difficult and the court only has to do the best it can using its common sense, as Lord Salmon said in the passage cited. Cases of this sort, where the disease manifests itself many years after the exposure, present great problems, because much of the detail is inevitably lost. I can see that in Borel's case where the defendants were manufacturers as opposed to employers the position may be particularly difficult. But in my view the court must do the best it can to achieve justice, not only to the claimant but the defendant, and among defendants.
21. This was the approach adopted by Mustill J. in Thompson v Smiths Shiprepairers [1984] 1 QB 405. The plaintiffs in test actions had been engaged in the ship repair industry where they had been exposed to excessive noise over extended periods of their employment which had resulted in deafness. The problem arose because all excessive noise had contributed to their disability, but the defendant employers were not guilty of negligence until 1963, by which time considerable damage had been done, though it was not necessarily recognisable. There was also the problem of successive employers. Mustill J. dealt with the issue at p437 to 444. He rejected similar arguments to those raised by Mr. May on the basis of the Bonnington and McGhee cases. The passage is too long to cite in full though I respectfully agree with it. I refer only to two passages. At p443D Mustill J. said:
"The defendants as well as the plaintiffs are entitled to a just result. If we know - and we do know, for by the end of the case it was no longer seriously in dispute - that a substantial part of the impairment took place before the defendants were in breach, why in fairness should they be made to pay for it? The fact that precise quantification is impossible should not alter the position."
And at G:
"Thus, whatever the position might be if the court were to find itself unable to make any findings at all on the issue of causation and was accordingly being faced with a choice between awarding for the defendants in full, or for the plaintiffs in full, or on some wholly arbitrary basis such as an award of 50 per cent., I see no reason why the present impossibility of making a precise apportionment of impairment and disability in terms of time, should in justice lead to the result that the defendants are adjudged liable to pay in full, when it is known that only part of the damage was their fault. What justice does demand, to my mind, is that the court should make the best estimate which it can, in the light of the evidence, making the fullest allowances in favour of the plaintiffs for the uncertainties known to be involved in any apportionment. In the end, notwithstanding all the care lavished on it by the scientists and by counsel I believe that this has to be regarded as a jury question, and I propose to approach it as such."
22. The particular difficulty in Thompson's case was that, as the graph at Annex B to the judgment shows the progression of the disease is not constant, but is greater in the early years of exposure. On the other hand it is loss of the higher frequencies which tends to happen later that causes greater handicap and the noise induced deafness is additional to the deafness as a result of natural ageing, and has therefore greater impact on the disability in later years. There is no such problem here since the progression is linear depending on the amount of dust inhaled. All dust contributes to the final disability.
23. This was the approach that the judge adopted here. But it is said by Mr. May that there is no evidence to support his conclusion or justify the deduction of 25%. I do not agree. Although it is only a question of nomenclature I think Mr. Goldstaub is right when he submits that it is not so much a question of apportionment between tortfeasors as one of proof of causation in respect of a quantifiable part of his disability by the claimant against the defendant; and further it was not so much a question of discounting the full liability figure, as counting the proportion attributable to the defendant. But this is somewhat semantic and does not affect the judge's approach and conclusion.
24. In my judgment there was ample evidence to support the judge's conclusion. Not only was there the evidence of Dr. Page and Dr. Howard which I have already referred to in paragraphs 7, 8 and 9, but it was the case that Mr. May was himself putting in cross-examination to Dr. Page. At p16B Mr. May asked this:
" Q. So far as cause and material contribution are concerned, may I ask you this? It is right, is it not, that if there is substantial exposure with employer number 1 over, say, 5 years and substantial exposure with employer number 2 over 5 years, each in medical knowledge is taken to have materially contributed to the disease?
A. Yes."
A little earlier Mr. May put to Dr. Page passages from an article by Dr. Mereweather, an acknowledged expert in the field in the Journal of Industrial Medicine. At p13E he said :
"It is helpful to visualise fibrosis of the lungs as it occurs among asbestos workers as the slow growth of fibrous tissue between the air cells of the lungs wherever the inhaled dust comes to rest. While new fibrous tissues is being laid down like a spiders web that deposited earlier gradually contracts. This fibrous tissue is not only useless as a substitute for the air cells, but with continued inhalation of the causative dust, by its invasion of new territory and consolidation of that already occupied it gradually, and literally strangles the essential tissues of the lungs. In common with other essential organs of the body the lungs have a large reserve of tissue for use in emergencies and to permit of a diminution in functional capacity due to advancing age or disease. For this reason, and because fibrosis of the lungs is essentially a local disease, it is only when the fibrosis progresses to the extent of obliterating this reserve, that undue shortness of breath on any extra effort draws the worker's attention to the fact that his health is not what it should be. The other symptoms of the disease such as cough are equally unassuming, and are readily ascribed to some common and trivial cause. From this point the progress of the disease is more rapid, since it is now encroaching on the remaining sound tissue of the lungs, already only just sufficient to maintain him in his ordinary daily activities. Ultimately, if no acute respiratory infection has precipitated a fatal termination, a stage is reached when the lungs can do little more than maintain life, and the shortness of breath becomes extreme."
Dr. Page agreed.
And at p14C there is further citation from Dr. Mereweather:
"Q......This disease, insidious in its onset, stealthily advances with but faint warnings of its progress; inexorably it cripples the essential tissues of the lungs, yet for a considerable period causes almost now inconvenience to the worker.
Pausing there, is that right?
A. Inexorably cripples the essential tissues of the lungs. Well, it gets worse progressively."
25. It might be said that the judge should have made the defendants liable only to 50%. If the other employers had been before the court, then subject to exposure which ought to be considered de minimis, I think this is what he would have done. As it is he erred on the side of generosity to the claimant. No one criticises him for that. This method of dividing responsibility on a time exposure basis is, I understand, adopted among insurers in such cases as these. In the absence of some unusual feature, such as for example periods of exposure to a particularly dangerous blue asbestos during some periods, that seems to me to be not only the sensible, but correct approach in law. In practice, many years afterwards, such distinctions are likely to be impossible to prove.
26. For these reasons I would dismiss this appeal.
LORD JUSTICE MUMMERY:
27. I agree with the judgment of Lord Justice Stuart-Smith.
LORD JUSTICE CLARKE:
28. I also agree that this appeal should be dismissed, but I add a few words of my own because I do not entirely agree with the approach to this class of case which is proposed by Stuart-Smith LJ.
29. I entirely agree that, for the reasons given by him, this court should not interfere with the judge's decision on the procedural aspects of the case. Even though the defendants should in my view have pleaded their case that others had contributed to the claimant's condition, by the end of the trial there was ample material to enable the judge to decide the matter justly. I also agree with Stuart-Smith LJ that in this class of case the defendant is liable in respect of the contribution that its negligence or breach of duty has made to the claimant's condition and that in reducing the damages by 25 per cent, the judge erred on the side of generosity to the claimant. It was open to the judge to hold that the defendants had shown on the evidence that at least 25 per cent of the claimant's disability was not their responsibility but that of others. On the facts found the judge's conclusion was, in my opinion justified and, for that reason, I too would dismiss the appeal.
30. The point on which I regret that I am unable to agree with Stuart-Smith LJ relates to burden of proof. In short, I prefer the view expressed by Longmore J in the passage which has been quoted from his judgment in Milner v Humphreys and Glasgow Ltd. My reasons are shortly as follows.
31. The burden of proving that the defendants' negligence or breach of duty caused the relevant injury or condition is on the claimant: Bonnington Castings Ltd v Wardlaw [1956] AC 613, Nicholas v Atlas Steel Foundry and Engineering Co Ltd [1957] 1 WLR 613, McGhee v National Coal Board [1973] 1 WLR 1 and Wilsher v Essex Area Health Authority [1988] AC 1074. The claimant discharges that burden by proving that the defendant's negligence or breach of duty made a material contribution to his injury or condition. Thus, for example in Wilsher Lord Bridge described the decision in Bonnington Castings in this way (at page 1086B):
"Their Lordships concluded, however, from the evidence that the inhalation of dust to which the pursuer was exposed by the defendant's breach of statutory duty had made a material contribution to his pneumoconiosis which was sufficient to discharge the onus on the pursuer of proving that his damage was caused by the defender's tort."
He added that the next year, in Nicholson, the House of Lords held, in another case of pneumoconiosis, that the employers were liable for the employee's disease arising from the inhalation of dust from two sources, one `innocent' and the other `guilty' on facts virtually indistinguishable from those in Bonnington.
32. It is I think at least arguable on the basis of those decisions that in a case of this kind, where the claimant proves that two employers have made a material contribution to his condition, he is entitled to judgment in full against each, leaving them to contest issues of contribution between them. That would certainly be the case where the injury was truly indivisible, so that each made a material contribution to the same damage, as in a case of damage caused by, say, a collision. However, in this class of case, as Longmore J observed, the injury or disease is not truly indivisible, but is contributed to by sequential exposure to asbestos which aggravates the condition. In these circumstances, as Mustill J said in similar circumstances (albeit with regard to deafness) in Thompson v Smiths Shiprepairers (Norht Shields) Ltd [1984] QB 405 (at page 443D), in the first passage quoted by Stuart-Smith LJ:
"The defendants as well as the plaintiffs are entitled to a just result. If we know - and we do know, for by the end of the case it was no longer in seriously in dispute - that a substantial part of the impairment took place before the defendants were in breach, why in fairness should they be made to pay for it? The fact that precise quantification is not impossible should not alter the position."

In my opinion that approach applies to this class of case.
33. Assuming that to be correct, the question is whether, once the claimant has proved that the defendants' breach made a material contribution to his condition, he is entitled to judgment unless the defendant proves that a definable part of his condition was caused either by `innocent' asbestos or by `guilty' asbestos caused by others, as Longmore J thought, or whether, once the point has been raised by the defendant, the claimant is not entitled to anything unless he proves what part of his disease was caused by the defendants.
34. It seems to me that Longmore J's view is the more consistent with the approach in the cases. If the position were that the claimant cannot, as a matter of law, recover anything more than the contribution which the defendant has tortiously made to his disease, it does seem to me to be surprising that none of their Lordships mentioned the point in either Bonningtons or Nicholson. That seems to me to be so even though (as appears to have been the case) the point was not raised by counsel. Moreover, Mustill J's approach in Thompson also seems to me to be consistent with the conclusion that the burden of proof in this regard (whether classified as the legal burden or the evidential burden) is on the defendant. In the passage quoted above, he spoke in terms of what was known at the end of the trial and he said (at page 443H-444A), in the last part of the passage quoted by Stuart-Smith LJ:
"What justice does demand, to my mind, is that the court should make the best estimate which it can, in the light of the evidence, making the fullest allowances in favour of the plaintiffs for the uncertainties known to be involved in the apportionment. In the end, notwithstanding all the care lavished on it by the scientists and by counsel I believe that this has to be regarded as a jury question, and I propose to approach it as such."

It seems to me that it would not be appropriate to make `the fullest allowances in favour of the plaintiffs' if the burden of establishing the apportionment were on them and not on the defendants.

35. I do not share the view that justice demands that the burden on this question should be on the claimant. It seems to me that once the claimant has shown that the defendants' breach of duty has made a material contribution to his disease, justice requires that he should be entitled to recover in full from those defendants unless they show the extent to which some other factor, whether it be `innocent' dust or tortious dust caused by others, also contributed. It follows that I regard the part of the judgment of the Fifth Circuit of the United States Court of Appeals in Borel v Fibreboard Paper Products Corp (1973) 493 F2d 1076 at 1095 as expressing a just result and not an unjust result.
36. Just as the burden is on a negligent defendant to prove contributory negligence, so the burden should be on a negligent defendant who has contributed to the claimant's disease to show that others have also contributed and to what extent. I do not think that it matters in this regard whether such a burden is classified as a legal burden of proof or an evidential burden, the result will be the same and, in either event, in my opinion defendants must plead the point if they wish to rely upon it.
37. I should add, by way of postscript, that, although I have expressed a different view from that expressed by Stuart-Smith LJ, I entirely agree with him that in reality these cases should not be determined by onus of proof. That seems to me to be so whatever the correct view of where the burden of proof lies. That is because, as Mustill J put it in Thompson at page 443E,
The fact that precise quantification is impossible should not alter the position. The whole exercise of assessing damages is shot through with imprecision.
The assessment of questions of this kind are essentially jury questions which have to be determined on a broad basis, so that it will only in the rarest of cases that recourse need to be had to the burden of proof. Moreover, this is not such a case on the facts. I agree that the appeal should be dismissed.

Order: Appeal dismissed with costs, the amount payable to be, referred for detailed assessment in default of agreement. Legal Aid Taxation of Claimants costs. Permission to appeal was refused.
(Order does not form part of the approved judgment)