Mesothelioma: Causation. What constitutes a material increase in the risk?

The Claim

Mr Bannister’s widow claimed that in 1983 or 1984, when he was working as an accountant, Mr Bannister was culpably exposed to asbestos when office partition panels were removed by workmen, which left a visible residue of asbestos dust on his desk. She argued that this exposure had materially increased his risk of developing mesothelioma, which sadly caused his death in 2019.

The Defendant, Mr Bannister’s employer at the time, denied that the workmen had left asbestos dust behind, but conceded that if they had, this was in breach of the legal duty to reduce asbestos exposure to the lowest reasonably practicable level.  

It was denied however that any such alleged asbestos exposure had materially increased the risk of the disease.

The Decision

The Court decided that there was no breach of duty. On the balance of probabilities, after warning employees that the partition panels contained asbestos, the Defendant would have engaged specialist asbestos contractors to remove them. The specialists would be unlikely to have left behind visible residues of asbestos dust.

The replacement partitions contained no asbestos and the non-specialist contractors who fitted them were more likely to have left the dust behind, which would have been harmless.

In any event, the Court concluded that if the alleged exposure to asbestos had taken place, it would have been insufficient to have materially increased the risk of development of mesothelioma.

The Evidence

There were no contemporaneous documents to confirm when or how the work took place.

Mr Bannister, in video evidence given on commission before his death, and his former colleague Mr Ford, were found to be honest and straightforward witnesses. The Judge was mindful not to allow the Defendant “to convert one of the inherent difficulties in asbestos litigation – the inevitably long latency periods of the disease, into its first line of defence.” However the fallibility of human memory in general meant that the Judge confessed that he had “substantial doubt” as to whether Mr Bannister’s recollection of events could be relied upon.

Expert evidence was given by a forensic scientist and a consultant physician for the Claimant, and by an occupational hygienist and consultant physician for the Defendant.

The Judge found on the basis of the expert evidence that the alleged level of asbestos exposure would not have materially increased the risk of disease, even if that exposure had in fact occurred. Mr Bannister was not present when the work took place. The judge preferred the Defendant’s expert evidence to that of the Claimant’s on the likely level of exposure, acknowledging the experts’ calculations to be “at best an exercise in approximation.”

The Judge said that epidemiological evidence should be approached with caution, but had a limited role to play nevertheless. The Defendant’s expert view of there having been a 1 in 50 million annual increase in the risk of developing mesothelioma was accepted.


The case illustrates the difficulties often prevalent in asbestos claims in making factual findings about events occurring decades earlier, in the absence of contemporaneous documentation.

Ultimately it is for the Judge to find in each case on the facts whether there was a material increase in the risk of mesothelioma. Both sides’ experts accepted that the notional risk in this case was not a risk that an average patient should worry about, and the Judge regarded it as “incredibly small”.

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