Risky business: Navigating materiality, insignificance and the pitfalls of absolute risk in mesothelioma claims

Background

The judgment in Johnstone v Fawcett Garage [2025] EWCA Civ 467 provides a comprehensive analysis of the principles of materiality, the meaning of "insignificant risk” and the "absolute risk" approach in the context of mesothelioma claims.

The claim was brought by Alexander Johnstone (Personal Representative of the Estate of Elaine Johnstone) in respect of the Mrs Johnstone’s death due to mesothelioma. The claim was issued against Fawcett's Garage, where Mrs Johnstone had worked and allegedly been exposed to asbestos. Mrs Johnstone worked at Fawcett's Garage between 1982 and 1989, during which time she was alleged to have been exposed to asbestos fibres due to unsafe practices in the garage's workshop. The Claimant argued that this exposure materially increased the risk of Mrs Johnstone developing mesothelioma. HHJ Simon found that the increase in risk was "in the order of 0.1% or less" and concluded that this was not material. A decision which the Claimant then appealed.

The Judgment

The Court of Appeal upheld the decision of HHJ Simon, finding that the increase in risk was de minimis and thus not material. The Court of Appeal examined the expert evidence, particularly the Hodgson & Darnton Study relied upon by Professor Jones, which suggested that, at very low levels of exposure, the risk of developing mesothelioma from chrysotile asbestos was "probably insignificant". The Court of Appeal accepted that HHJ Simon was entitled to rely on this evidence, provided it was approached with caution. Caution was required as the H&D Study was a meta-analysis of various studies of mortality risk based upon exposure to high levels of asbestos, whereas this case involved very low level exposure and so involved an exercise in extrapolating down from the study’s findings to determine likely risk in the current case. The claimant’s criticism of Professor Jones’ use of the H&D Study was rejected.  

The Court of Appeal also considered the "absolute risk" approach, which involves assessing whether the risk of developing mesothelioma from the defendant's breach is medically significant in absolute terms. The Court of Appeal, whilst recognising the extensive expertise of the defendant’s medical expert, considered that adopting an “absolute risk” approach would be inconsistent with the special rule of causation established by Fairchild v Glenhaven Funeral Services Ltd [2002] UKHL 22 and Sienkiewicz v Grief (UK) Ltd [2011] UKSC 10. The “special rule” being that the court should consider whether a defendant’s breach materially increased the risk of contracting mesothelioma rather than whether the absolute risk was significant.

Consideration of Bannister

In reaching its decision, the Court of Appeal acknowledged the case of Bannister v Freemans Public Limited Company [2020] EWHC 1256 (QB), where the “absolute risk” approach had been considered. However, the Court of Appeal did not follow the approach taken in Bannister. The judgment notes that Bannister was concluded in circumstances where no epidemiological expert evidence was before the judge, whereas, in Johnstone, extensive epidemiological expert evidence was available. The judge in Bannister, having no epidemiological evidence before him, concluded that the exposure was de minimis and so had not materially increased the risk of mesothelioma, on the basis of medical evidence which described the dose as “medically insignificant.” The Court of Appeal was not bound by Bannister and, crucially, did have the benefit of epidemiological evidence.  

Comment

In rejecting an "absolute risk" approach, as endorsed in Bannister, the Court of Appeal encourages defendants to ensure that epidemiological evidence is adduced in low exposure cases, to consider and contrast the occupational risk from the background risk and determine whether the increase in risk caused by that occupational exposure is low enough to be disregarded or high enough to be considered material. Such an approach will inevitably increase legal costs, and it is perhaps to be regretted that the rather more straightforward approach of inviting the medical expert to consider whether, in absolute terms, the increase in risk is so tiny that it should be disregarded as being non-material, has been discouraged. Given that the Court of Appeal upheld the trial judge's assessment on materiality, however, a judgment founded on consideration of the epidemiological evidence (described by the Court of Appeal as a "direct risk" approach), its comments on the "absolute risk" method adopted in Bannister were obiter.