The Supreme Court today handed down its judgments in two linked mesothelioma appeals: Grief (UK) Ltd v Sienkiewicz and Knowsley MBC v Willmore  UKSC 10. In doing so it made a number of important findings on the law of causation in tort generally as well as the special Fairchild rule applicable in mesothelioma cases. It also doomed counsel appearing in future industrial disease cases to the embarrassment of likely mispronunctiation of the name of the claimant in the Sienkiewicz case.
The feature shared by the two cases was that the claimant identified a single environment in which he was exposed to low levels of asbestos by the actions of a single defendant. Such cases are termed, potentially misleadingly, "single exposure" cases. They are to be contrasted with "multiple exposure" cases in which a claimant is exposed, either concurrently or consecutively, to exposure in different environments and/or for which different defendants are responsible.
As is well-known, in Fairchild the House of Lords concluded that it was impossible in the current state of scientific understanding (as is still the case) to prove on the balance of probabilities that a particular defendant caused mesothelioma in multiple exposure cases. That therefore justified a departure from the normal requirement to prove that it was more likely than not that the defendant caused or contributed to the onset of a disease, and led the House to rule that demonstrating that a defendant had materially increased the risk would establish liability.
In Barker, the House decided that the logical consequence of this was that a defendant should only have to pay an aliquot share of damages in line with the degree to which, in multiple exposure cases, he had increased the risk of contracting mesothelioma. However, Parliament swiftly intervened to provide, by s3 of the Compensation Act 2006, that a defendant would have to pay full damages.
In the two cases under appeal, it was argued that in a single exposure case, the only competing causes were general environmental exposure which, rather worrying, all of us who live in cities apparently have (see Fairchild at  per Lord Bingham) or exposure unknown and unidentified. It should be necessary for a claimant to prove that the exposure to asbestos by the defendant at least doubled the risk of the claimant contracting mesothelioma.
The origin of this argument lies in the science of epidemiology or the statistical analysis of the correlation between events in order to establish causes and effects. To those who have never worked as hard in their lives as they had to do to get a Maths A-level (ie me), Lord Phillips' judgment contains a reasonably comprehensible account of the significance of a doubling of risk: at -. In the Sienkiewicz case, the trial judge had concluded on the basis of the expert evidence that the exposure of claimant to asbestos in the defendant's employment had increased the risk by 18%. No such conclusion was reached in the Willmore case of very slight exposure from a number of sources while the claimant was a pupil at the local authority's secondary school.
The Supreme Court, sitting in a panel of seven, unanimously rejected the principle that in a "single exposure" case, a doubling of the risk would need to be demonstrated. Rather frustratingly, each member of the court decided it was necessary to give a judgment and this will no doubt lead to detailed dissection of the decision in future cases. The main judgments were given by Lord Phillips and Lord Hope.
First, they disagreed with the Court of Appeal's view in Sienkiewicz that the defendants' arguments were precluded by the 2006 Act. It was pointed out that all s3 did was to reverse Barker and require a defendant found to have exposed a claimant to asbestos to pay full damages rather than a proportion. It did not enshrine the Fairchild rule on causation into statute: at , -.
However, following a detailed consideration of the main decisions on causation, they held that Fairchild applied in a single exposure case: at -, -. Accordingly, the fact that only one source of exposure can be identified does not prevent a claimant establishing liability on the basis of showing that an exposure is material.
The court also unanimously rejected an alternative argument that unless the risk of mesothelioma was doubled, the exposure could not be "material" for the purposes of Fairchild: at , .
The judgment of the Supreme Court is also of relevance to the law of causation in relation to other industrial diseases and more generally. First, Lord Phillips gave guidance as to the role of the 'doubling of risk' principle in relation to different types of case:
90. For reasons that I have already explained, I see no scope for the application of the "doubles the risk" test in cases where two agents have operated cumulatively and simultaneously in causing the onset of a disease. In such a case the rule in Bonnington applies. Where the disease is indivisible, such as lung cancer, a defendant who has tortiously contributed to the cause of the disease will be liable in full. Where the disease is divisible, such as asbestosis, the tortfeasor will be liable in respect of the share of the disease for which he is responsible.
91. Where the initiation of the disease is dose related, and there have been consecutive exposures to an agent or agents that cause the disease, one innocent and one tortious, the position will depend upon which exposure came first in time. Where it was the tortious exposure, it is axiomatic that this will have contributed to causing the disease, even if it is not the sole cause. Where the innocent exposure came first, there may be an issue as to whether this was sufficient to trigger the disease or whether the subsequent, tortious, exposure contributed to the cause. I can see no reason in principle why the "doubles the risk" test should not be applied in such circumstances, but the court must be astute to see that the epidemiological evidence provides a really sound basis for determining the statistical probability of the cause or causes of the disease.
93. Where there are competing alternative, rather than cumulative, potential causes of a disease or injury, such as in Hotson, I can see no reason in principle why epidemiological evidence should not be used to show that one of the causes was more than twice as likely as all the others put together to have caused the disease or injury.
What amounts to a "material" exposure has caused some difficulty for practitioners since Fairchild was decided. Lord Phillips gave some useful guidance. He pointed out the importance of comparing the exposure for which the defendant was responsible with the total exposure: at . It remains a question of fact in all cases, but the test is not a high one. At  he said:
The reality is that, in the current state of knowledge about the disease, the only circumstances in which a court will be able to conclude that wrongful exposure of a mesothelioma victim to asbestos dust did not materially increase the victim’s risk of contracting the disease will be where that exposure was insignificant compared to the exposure from other sources.
The court also made some general comments about the law of causation in personal injury cases. Varying comments are made by the court as to epidemiological evidence generally: besides Lord Phillips' comments quoted above, see at , -, -, -. Effectively, the weight to be given to such evidence will continue to depend on its content and the context in which it is adduced.
Some fairly strong comments were made by Lord Brown, in particular stating at  that the Fairchild principle should not be extended beyond mesothelioma cases. They cannot, however, be regarded as part of the ratio of the decision.
Overall, the decision is a welcome one to the practitioner; if the appellants had succeeded, then "single exposure" cases would have more frequently called for complex engineering and statistical evidence which can only ever give an approximate answer to the question posed. Clearly it will be unwelcome to insurers. There is, however, a crumb of comfort for defendants in the observations on the challenges to the factual inferences drawn by Nicol J in Willmore, which had partly succeeded in the Court of Appeal. The inferences were described as "truly heroic" by Lady Hale at  and as having a "slender and speculative basis" by Lord Mance at . Lord Rodger gave this warning at :
Especially having regard to the harrowing nature of the illness, judges, both at first instance and on appeal, must resist any temptation to give the claimant’s case an additional boost by taking a lax approach to the proof of the essential elements. That could only result in the balance struck by the Fairchild exception being distorted.
This merely echoes the earlier decision in Brett v University of Reading  EWCA Civ 88, para 26, where Maurice Kay LJ said:
Fairchild exceptionally relieves a claimant who has proved exposure and breach of duty from having to prove causation. What it does not do is to relieve him from proving the other elements. As Lord Justice Sedley has demonstrated, the evidence in this case sufficiently established exposure in the course of employment at Reading University but it did not begin to establish a breach of duty on the part of the university.
With the incidence of mesothelioma, sadly, not expected to peak in the UK for at least another decade, it is unlikely that the Sienkiewicz decision will be the last word on the subject of causation in mesothelioma claims.