On 9 March 2011, the Supreme Court handed down its judgment in the joint appeal of Sienkiewicz v Grief (UK) Ltd; Knowsley MBC v Willmore [2011] UKSC 10. The seven-judge bench, consisting of Lord Phillips, Lord Rodger, Lady Hale, Lord Brown, Lord Mance, Lord Kerr and Lord Dyson, unanimously dismissed both appeals and upheld the decision of the Court of Appeal that the Fairchild exception to the conventional rule on causation, which applies in “multiple exposure” mesothelioma cases (that is, where the claimant has contracted mesothelioma after being wrongly exposed to asbestos by several defendants) also applies to “single exposure” cases (involving a single tortious defendant and other non-tortious or environmental exposure to asbestos). 

The effect of this is that the claimant in cases of single exposure does not need to show that the defendant’s breach of duty doubled the risk of developing the disease, and needs only to show that it materially increased the risk to the claimant of contracting mesothelioma.


In Sienkiewicz, the claimant was the administratrix of the estate of her mother, Enid Costello.  Enid Costello had died of mesothelioma in 2006 aged 74 having worked for the defendant, Greif (UK) Limited (“Greif“) (and the predecessors of Greif) in an office at a steel drum factory for 18 years between 1966 and 1984.  Exposure at the factory was light but continued for a prolonged period and was calculated by the trial judge to have increased Enid Costello’s risk of catching mesothelioma by 18%.  Enid Costello was also subject to general low-level atmospheric exposure.

In Willmore, Mrs Willmore died of mesothelioma in 2009 aged 49 and was found to have been exposed to asbestos at her secondary school which was run by the appellant, Knowsley Metropolitan Borough Council (the “Council“).  As well as the allegedly tortuous exposure, Mrs Willmore was exposed to low-level, non-tortious, atmospheric asbestos.

The Fairchild Exception and Barker

The House of Lords decision in Fairchild v Glenhaven Funeral Services Ltd [2002] UKHL 22 relaxed the conventional rule of causation (that is, that a claimant must show that it is more likely than not that the harm suffered was caused by the defendant’s breach of their duty of care) in mesothelioma cases where there have been multiple exposures.  This is because medical science cannot currently determine which asbestos fibre or fibres causes the mesothelioma to develop in cases where there have been multiple exposures, as it usually develops some years after the initial exposure.  Accordingly, the House of Lords regarded it impossible for the claimant to prove the liability of a single defendant by applying the conventional “but for” test, which would cause injustice to the claimant.

The Fairchild decision was made in the context of claims against multiple employers who were each found to be in breach of their duty of care to the claimant  and the Fairchild exception provides that defendants that breach their duty of care “materially increase the risk” of mesothelioma and should therefore be jointly and severally liable for the damage suffered if the disease does develop.  However, the case left it unclear as to whether the exception would apply where the other possible sources of injury were not other breaches of duty but a lawful act or a natural occurrence, for example, low-level background exposure.

The Fairchild exception was refined in Barker v Corus [2006] UKHL 20 so that each responsible party was only liable for the proportion of damages which correlated to their contribution to the risk to the claimant.  This apportionment of damages was then overturned by Parliament through the  implementation of section 3 of the Compensation Act 2006 (the “Act“), which is specific to cases of mesothelioma and provides that each “responsible person” will be liable for the whole of the damage caused to the victim and such liability will be joint and several with any other liable party.

Section 3 of the Compensation Act 2006

3. Mesothelioma: damages

(1)        This section applies where—

(a)        a person (“the responsible person”) has negligently or in breach of statutory duty caused or permitted another person (“the victim”) to be exposed to asbestos,

(b)        the victim has contracted mesothelioma as a result of exposure to asbestos,

(c)        because of the nature of mesothelioma and the state of medical science, it is not possible to determine with certainty whether it was the exposure mentioned in paragraph (a) or another exposure which caused the victim to become ill, and

(d)        the responsible person is liable in tort, by virtue of the exposure mentioned in paragraph (a), in connection with damage caused to the victim by the disease (whether by reason of having materially increased a risk or for any other reason).

(2)        The responsible person shall be liable—

(a)        in respect of the whole of the damage caused to the victim by the disease (irrespective of whether the victim was also exposed to asbestos—

(i)         other than by the responsible person, whether or not in circumstances in which another person has liability in tort, or

(ii)         by the responsible person in circumstances in which he has no liability in tort), and

(b)        jointly and severally with any other responsible person

Decisions Below

The trial judge in Sienkiewicz dismissed the claim for damages and held that the Fairchild exception did not apply in single exposure cases.  It was held that, since Grief’s tortious exposure only increased the risk of developing mesothelioma by 18%, the claimant had failed to establish on a balance of probabilities that the tortious exposure was the likely cause of Mrs Costello’s disease.  However, the judge considered that a difficult point of law arose and granted permission to appeal.

In Willmore, the trial judge held that the Council was liable on the ground that it contributed materially to the claimant’s exposure to airborne asbestos fibres. The Council’s appeal involved an attack on findings of fact by the judge that it was responsible for exposing Mrs Willmore to sufficient asbestos dust to cause a material increase in risk.

The Court of Appeal (Smith LJ presiding; Scott Baker LJ and Lord Clarke) considered the “doubles the risk” test (that is, that it had to be proven that the exposure for which Greif was responsible had more than doubled the environmental exposure) which Greif’s Counsel submitted had to be proved in order to satisfy the balance of probabilities test, .  The Court of Appeal first considered this in relation to diseases other than mesothelioma and stated obiter than, in a case of multiple potential causes, a claimant can demonstrate causation by showing that the tortious exposure has at least doubled the risk arising from the non-tortious cause(s).  However, Smith LJ held that this test could not be applied in relation to mesthelioma, citing section 3(1)(d) of the Act (see above) and stating that, by enacting this section, Parliament had ruled that causation in mesothelioma cases could be established by proof of a material increase in risk only and therefore the defendant was unable to try and rely on the “doubles the risk” common law test as a means of avoiding liability and as a consequence, the Fairchild test should be applied.

Supreme Court Decision

Greif appealed against the Court of Appeal’s decision on two interrelated grounds: (i) that the exposure it was responsible for only increased Mrs Costello’s total amount of exposure experienced by 18% (rather than almost doubling the exposure) and therefore the respondent had failed to prove on balance of probabilities that Greif caused Mrs Costello’s mesothelioma; and (ii) that occupational exposure to asbestos dust would only constitute a “material increase” in risk for the purposes of the Fairchild rule if it more than doubles the environmental exposure to asbestos dust endured by the victim.  Counsel for Greif also argued that the Court of Appeal erred in holding that section 3 of the Act allowed the application of the Fairchild rule of causation in mesothelioma cases.

In the main Supreme Court judgment, Lord Phillips considered that knowledge about mesothelioma is based partly on medical science and partly on statistical analysis, or epidemiology, and, after due consideration, concluded that epidemiological evidence alone is not a satisfactory basis for making findings of causation in cases of mesothelioma because of medical uncertainties as to its cause, the long latency of the disease, the limited time between the first experience of symptoms and death and the fact that the data of victims exposed to a substantial amount is extrapolated with the data of victims who have had very light exposure.

As regards the medical uncertainties, Lord Phillips explained that there is uncertainty as to whether the contraction of mesothelioma in the first instance is related to the amount of asbestos fibres ingested but that mesothelioma is an indivisible disease, meaning that it is caused by a single agent and its severity bears no relation to the amount of asbestos fibres ingested.  Unlike a divisible disease, for example, pneumoconiosis, where the severity depends on the quantity of silica inhaled (as in Bonnington Castings Limited v Wardlaw [1956] AC 613), it is difficult to apportion responsibility into shares of liability.

The main issues the Supreme Court addressed were as follows:

  1. Section 3 of the Act

Lord Phillips interpreted section 3(1)(d) of the Act slightly differently to Smith LJ in the Court of Appeal and held that it did not automatically make a defendant liable in tort if he has materially increased the risk of a victim contracting mesothelioma.  Lord Phillips held that the section only applies in order to establish quantum where liability has already been established.  As Lord Rodgers stated in his judgment, liability may be established on the basis that the defendant has materially increased the risk to the claimant but the wording of the section 3(1)(d) of the Act also provides that liability could be “for any other reason“.  The section therefore does not preclude the courts from reverting to the conventional approach to causation on a balance of probabilities in mesothelioma cases should advances in medical science in relation to the medical origin of mesothelioma make such a step appropriate.

  1. Epidemiology and the nature of the “doubles the risk” test

Lord Phillips explained that the “doubles the risk” test applies epidemiological data to determine causation on a balance of probabilities where science does not make it clear how and when an injury was caused.  Epidemiology is the study of the occurrence and distribution of events over human populations in order to find possible statistical associations between the events.  Such analysis is based on the calculation of the relevant risk (“RR“) arising from any particular type of exposure, with an RR of 1 indicating that there is no association between the particular exposure and the risk and an RR of 2 indicating the particular exposure doubled the chance that the victim would contract the disease.  An RR of above 2 would mean that the statistical likelihood is that the particular exposure was the cause of the disease.  Lord Phillips questioned the reliability of epidemiological data, stating that an RR of just over 2 is a tenuous basis for concluding that the probable statistical cause was also the probable biological cause because of the fine nature of the balance of probability in such circumstances.

  1. Can the “doubles the risk” test be applied in multiple cause cases involving diseases other than mesothelioma?

In response to Smith LJ’s obiter observation that the “doubles the risk” test can be applied in non-mesothelioma multiple cause cases, Lord Phillips did not consider this test applicable where there are two or more possible causes since, where a disease is indivisible, a tortious defendant will be liable in full and, where it is divisible, a defendant will be liable in respect of the share for which he is responsible.

Where contraction of a disease is dose-related and therefore there have been consecutive exposures to an agent or agents that cause the disease, the position in relation to the “doubles the risk” test will depend upon which exposure came first in time.  Where the innocent exposure came first, this test may be applicable (for example, in McGhee v National Coal Board [1973] 1 WLR 1, where the initial exposure of the claimant workman to the defendant’s brick kiln was not deemed tortious, but it was the subsequent lack of shower facilities, resulting in the workman having to cycle home caked in kiln dust and subsequently develop dermatitis, that was deemed to be so). 

  1. Can the “doubles the risk” test be applied in mesothelioma cases?

Lord Phillips held that, until medical science can clearly demonstrate the origin of mesothelioma, epidemiological evidence alone has not been considered by the courts as an adequate basis for making findings of causation.

  1. What constitutes a material increase in risk?

The Court held that liability for mesothelioma falls on anyone who has materially increased the risk of the victim contracting the disease and that an increase was “material” if it was not de minimis. What was de minimis would be a question for the judge on the facts of each particular case.  Lord Phillips reasoned that, had the trial judge in Siekiewicz considered that an 18% increase in risk was de minimis, he would have said so and therefore it could be concluded that the increase in risk was material in this current appeal.

The Supreme Court unanimously held that the trial judge in Sienkiewicz incorrectly applied the “doubles the risk” test.  Lord Phillips held that Greif’s wrongful exposure of Enid Costello to asbestos could not be held as statistically insignificant or de minimis since expert evidence provides that there is no known lower threshold of the exposure that is capable of causing mesothelioma and thus a very low level of asbestos exposure would suffice to cause the disease.

As regards Willmore, the Supreme Court considered that the trial judge’s finding of fact were very generous to Mrs Wilmore and Lord Mance even went so far as to say that exposure was found on a “slender and speculative basis“. However, the Court concluded that the criticisms to the trial judge’s findings of fact would not justify the Court in taking the “exceptional step” of disturbing the findings of fact of the courts below.

Both appeals were therefore dismissed.


The decision in this joint appeal may seem draconian in holding a sole defendant who may have exposed the claimant to a very low level of asbestos, which was then exacerbated by other environmental or otherwise non-tortious asbestos exposure, liable for the full amount of damages suffered by the victim.  However, as Lady Hale commented in her judgment, there was no way of allowing the appeal without reversing Fairchild and imposing the conventional “but for” rule on all such cases of mesothelioma going forwards.  The Court was reluctant to do this for several reasons, including the “rock of uncertainty” of the medical causation of mesothelioma.  Lady Hale commented that, even if the Court thought it right to reverse Fairchild, Parliament would soon reverse this decision in turn for policy reasons related to the dangerousness of asbestos and the hideousness of mesothelioma as a disease.

However, the Court did leave space for the reversion to the conventional causation test in future should scientific advancements make it possible to clearly distinguish between the different causes of mesothelioma.  In the meantime, due to the imprecise nature of the medical causation of mesothelioma, the way is potentially wide open for sole defendants, and their insurers, in “low-level” asbestos exposure cases to face full liability for damages despite other potential causes; mesothelioma claims could now be considered a lost cause from the defendant’s perspective unless the claimant has in some way negligently contributed to their exposure.

Furthermore, the obiter of Lords Phillip and Rodger in relation to the unsuitability of the “doubles the risk” test to non-mesothelioma cases may come to bear on future judgments related to this issue.  Still, the obiter warning of Lord Brown against creating further exceptions to the conventional rules on causation may stay in the minds of judges having to consider complex issues of causation in future: “the law tampers with the “but for” test of causation at its peril“.