Material contribution is always a hot topic in the field of medical negligence. This has been highlighted by the recent decision of CNZ v Royal Bath Hospitals NHS Foundation Trust & The Secretary of State for Health and Social Care, a decision which provided commentary on injuries from both tortious and non-tortious causes and whether non-negligent damage could and should be divisible from negligent damage. Further clarity on what needs to be proven to succeed with arguments that a breach of duty materially contributed to the damage suffered, where there are a range of potential negligent and non-negligent causes, was recently provided by the Court of Appeal in the industrial disease case of Michael Holmes v Poeton Holdings Limited [2023] EWCA Civ 1377. The decision provides helpful commentary on the need for a causative link between the breach of duty and the outcome itself.


Mr Holmes was diagnosed as suffering with early onset Parkinson’s disease in 2014. The aetiology of Parkinson’s disease is still unclear, but it is widely accepted that a combination of both genetic and environmental factors play a role in its development. Mr Holmes brought a claim against Poeton Holdings Limited (“Poeton”), his previous employer, for various breaches of duty between 1982 and 1997 which exposed him to unsafe levels of Trichloroethylene (“TCE”), a neurotoxic substance which can damage dopaminergic neurons. It is damage to these neurons which leads to Parkinson’s disease. Mr Holmes argued that exposure to unsafe levels of TCE materially contributed to the development of his Parkinson’s disease. It was Mr Holmes’ case that Parkinson’s disease was an indivisible injury (ie. one which was not dose related, unlike a divisible injury where each exposure to an agent will cause additional damage) and therefore, as the negligent exposure to TCE contributed to its cause, Poeton should be liable for all losses arising from it. Poeton argued that the exposure to TCE may have caused an increased risk of Mr Holmes developing Parkinson’s disease but the evidence did not show that exposure to TCE was capable of causing Parkinson’s disease.

At first instance, His Honour Judge Harrison found various breaches of duty which had exposed Mr Holmes to TCE. He concluded that this exposure to TCE created a material contribution to the risk of the Claimant sustaining injury and that on the balance of probabilities Mr Holme’s Parkinson’s disease was materially contributed to by the tortious TCE exposure. Despite the acceptance that Mr Holmes had a genetic predisposition to Parkinson’s disease, the Judge at first instance concluded that Poeton was liable for all consequences of the Claimant’s Parkinson’s disease as it was an indivisible injury. Poeton appealed the decision on the basis the Judge had failed to set out whether Mr Holmes would have developed Parkinson’s disease in any event, and therefore the exposure to TCE made no difference, noting that it was not shown that the exposure had caused the contraction of the disease. It was Poeton’s case that Mr Holmes could only establish a material contribution to the risk of Parkinson’s disease, rather than his Parkinson’s developing.

The Court of Appeal Decision

The Court of Appeal agreed that Parkinson’s disease is an indivisible injury, given that once it has been contracted its severity is not influenced by tortious/non-tortious events. The Court clarified that the Bonnington Castings v Wardlaw [1956] 1 AC 613 test, that the breach of duty must have caused or materially contributed to the injury itself (rather than the risk of the injury) applies to cases where there is an indivisible injury. Specifically, the Bonnington test applied as the tortious exposure of TCE was said to be contributing to the onset of the Parkinson’s disease, rather than severity of it, and there must therefore be a link between the TCE and the Parkinson’s disease.

The Court of Appeal held that whilst the Judge was entitled on the evidence to decide that it was possible that TCE was the cause of the Claimant’s Parkinson’s disease, the evidence only established that TCE was a risk factor and there was no evidence to prove causation between TCE and Parkinson’s disease. Given Parkinson’s disease is an indivisible injury, a risk factor was not sufficient and there needed to be evidence of a causative link between the breaches of duty and the injury. Merely proving tortious exposure, which could possibly cause the injury, does not prove a causative link ie. a plausible mechanism is not sufficient to prove material contribution. Ultimately, the Court of Appeal found that given the range of other genetic and environmental causes which could have caused Mr Holmes’ Parkinson’s disease, the evidence did not justify the conclusion that the wrongful exposure made a material contribution to the outcome. Essentially, the appeal succeeded because the science was not there to prove that the solvent actually played a role in Mr Holmes’ Parkinson’s disease.


This is another industrial disease case which adds to the growing list of precedent concerning material contribution. Its principles equally apply to cases of clinical negligence. The guidance from the Court of Appeal is helpful in clarifying that when dealing with an indivisible injury where there may be a number of both tortious and non-tortious causes, breach of duty has to be shown to have contributed to the injury itself, rather than the risk of the injury developing. It is not enough to succeed on material contribution, if the breach of duty is simply a risk factor for what actually transpired. The case highlights the need for experts to consider carefully whether diseases are divisible or indivisible and reminds us that there still has to be sufficient scientific basis for concluding that any negligent agent materially contributed to the onset of a disease. In a case where medical science is not sufficient to establish causation of an indivisible injury on a “but for” basis, a party may well find it is equally insufficient to prove material contribution.

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