The Supreme Court handed down its judgment in the joined cases of Sienkiewicz v Greif (UK) Ltd; Knowsley Metropolitan Borough Council v Willmore [2011 UKSC 10 on 9 March 2011. The issue in these cases was whether the exception (“the Fairchild exception”) developed by the House of Lords in Fairchild v Glenhaven Funeral Services Ltd [2002] UKHL 22 (“Fairchild”) applied in so-called “single exposure” cases where only one defendant is shown to have exposed the victim to low levels of asbestos, and where the only other known exposure is exposure to asbestos in the general atmosphere.

The House of Lords in Fairchild established the rule which provided that defendants whose breaches of their duty of care “materially increase the risk” of mesothelioma are jointly and severally liable for the damage suffered by persons wrongly exposed to asbestos if mesothelioma does in fact develop. Medical science cannot at present determine in multiple exposure cases which asbestos fibre (and therefore which employer) had caused the mesothelioma to develop, and thus merely demonstrating that a defendant had “materially increased” the risk would establish liability.

While Fairchild had involved multiple employers, it left open the question of whether the principle applied where other possible sources of injury were similar but lawful acts of someone else or a natural occurrence. In the subsequent case of Barker v Corus [2006] UKHL 20, the House of Lords decided that the logical consequence of this was that a defendant should only have to pay a share of damages in line with the degree to which he had increased the risk of the development of mesothelioma. Parliament then intervened to overturn this apportionment of damages by providing in section 3 of the Compensation Act 2006 that where a person was liable under the common law in tort to a victim who had contracted mesothelioma, that liability was for the whole of the damage caused by the disease, jointly and severally with any other responsible persons.

The claimants in this case were administrators of the estates of deceased victims who they alleged had been wrongly exposed to asbestos at their place of work, and school, respectively. In the first claimant’s case, the court at first instance concluded that the exposure to asbestos had been “very light”, resulting in a small increase of 18% and that, in the case of a single tortious exposure to asbestos, it was necessary for the claimant to prove the exposure had more than doubled the risk in order to make the respondent liable. The Court of Appeal, overruling this decision, held that a tortfeasor is liable for the development of mesothelioma where any exposure to asbestos had materially increased the risk of its development. The court in the second claimant’s case, in contrast, had initially found the exposure to asbestos had indeed materially increased the risk of the victim contracting mesothelioma, and this was upheld by the Court of Appeal. In the Supreme Court the respondents argued that where proceedings are directed against one party alone the Fairchild exception did not apply, and that liability could only be established if the claimant could show that the exposure had more than doubled the "background" risk of the mesothelioma.

Lord Phillips, delivering the judgment of the Supreme Court, held that the Fairchild exception applied to cases of mesothelioma involving a single defendant, and therefore the “doubles the risk” test for causation was therefore only potentially relevant in connection with the question of what constituted a material increase of risk. Summarising the scientific knowledge about the causation of mesothelioma he concluded that in light of the gaps in knowledge therein, it was not possible to decide causation on the basis of epidemiological evidence and therefore the concept of doubling that risk could have no application. Furthermore, comparing the statistical relationship between exposure and the incidence of the disease with the experience of the individual victim was particularly problematic in mesothelioma cases because of the very long latency period of the disease.

The appeals were thus dismissed.