Legal Update
Holmes v Poeton: indivisible diseases and material contribution
6 December 2023

Holmes v Poeton: indivisible diseases and material contribution

This article considers the recent decision of Holmes v Poeton [2023] EWCA Civ 1377 in respect of the application of the material contribution test for causation in indivisible injury cases.1 


Mr Holmes was negligently exposed to Trichloroethylene (‘TCE’) whilst employed by Poeton. Mr Holmes subsequently developed Parkinson’s disease. Mr Holmes brought a claim against Poeton on the basis that Poeton had materially contributed to the onset of his Parkinsons’ disease. The casual mechanism of Parkinson’s is poorly understood. Some of the scientific literature suggests exposure to TCE is causally linked to Parkinson’s. Other causes included genetic and environmental factors.  

Parkinson’s is an indivisible disease. Once it has onset, its severity, like lung cancer, is not proportional to the degree of exposure to the factors which contribute towards its onset. 


Where a disease is indivisible, and there are numerous causes that could contribute towards the onset of the disease, is the test for causation of damage by the Defendant’s breach to be assessed by reference to the ‘but for’ or ‘material contribution’ test? 


The decision of Stewart-Smith LJ Holmes turned primarily on his reading of what was decided in Bonnington.2 In Bonnington, the Defendant negligently allowed silica dust to emanate from swing grinders. However, silica dust also emanated from pneumatic hammers. The latter emanation was not a consequence of the Defendant’s negligence. The silica dust resulted in pneumoconiosis. Pneumoconiosis is a divisible disease. The more silica dust an individual is exposed to, the worse their pneumoconiosis will be.  

Nonetheless, on a close reading of the judgment in Bonnington, it is apparent that the House of Lords were, for whatever reason, treating pneumoconiosis as though it were an indivisible disease. Later authorities mistakenly relied on the fact that pneumoconiosis is a divisible disease to reach the conclusion that the ratio of Bonnington was that material contribution applies only to divisible diseases. Their focus should have been on how the House of Lords had characterized pneumoconiosis, rather than how pneumoconiosis ought to be characterized. Had they done so, they would have reached the conclusion that Bonnington is authority for the proposition that a material contribution can make out causation in an indivisible disease case.  

This view of Bonnington, Stewart-Smith LJ says, is confirmed by the Court of Appeal’s decision in Bailey. In Bailey, both the Defendant’s negligent care and the Claimant’s pancreatitis (which was not attributable to the Defendant’s breach) resulted in weakness. As a consequence of both factors, she was unable to clear her throat when she vomited. The Claimant aspirated her vomit, and then suffered a cardiac arrest and brain damage as a consequence. The Claimant claimed damages for the brain injury and cardiac arrest.  

The Court of Appeal in Bailey3 upheld the decision of the Judge at first instance4 that the Claimant need only prove that the Defendant’s negligence made a material contribution to the Claimant’s weakness, which ultimately caused the Claimant’s more significant injuries. Those injuries – cardiac arrest and brain injury – were indivisible. Thus, material contribution was applicable in indivisible injury cases.  

Despite Bailey and Bonnington establishing that material contribution could, in principle, be relied on to establish causation here, Mr Holmes’ claim failed as he was unable to prove that the TCE had made a material contribution to the onset of his Parkinson’s.  


  • Previously, there were inconsistent authorities on as to whether a claimant could make out causation in an indivisible injury case on the material contribution test rather than on a ‘but for’ basis.  
  • Following Holmes, causation can be made out in indivisible injury cases if the Defendant’s breach was one of a number of causes of the injury and the defendant’s breach materially contributed to the injury.  
  • The distinction between divisible and indivisible diseases will, however, remain important. Prior to Holmes, where the divisibility of a claimant’s injury was ambiguous, a claimant that sought to characterize their injury as indivisible was at risk that a judge would follow Thorley and require the claimant to prove ‘but for’ causation in order to win at trial. That risk no longer exists. Claimants will now seek to characterize their injury, where possible, as indivisible due to the more favourable rules of recovery.  
  • Where a claimant suffers from a divisible injury that was materially contributed to by a defendant’s breach, if it is possible to identify the extent to which the defendant’s breach materially contributed towards the injury, then the defendant is liable only for that portion of damage to which they contributed.5  
  • By contrast, where a claimant suffers from an indivisible injury, the defendant is likely6 liable for the whole of the injury caused, even where other factors contributed towards that injury. 
  • There will be some cases where the divisibility of the disease is not arguable. For example, it is widely accepted that asbestosis is divisible and mesothelioma is indivisible. Nonetheless, given that the extent of recovery will turn on whether a disease is characterised as divisible or indivisible, the next battleground in material contribution will likely be the distinction between the two.  
  • For example, the authorities differ in their characterization of the divisibility of the Claimant’s injuries in Bailey. In AB, the Court of Appeal said the injury was divisible. In Holmes, Stewart-Smith LJ says the injuries were indivisible. The difference between them is that whereas Holmes looks at the injuries which lie at end of the chain of causation, AB looked at the injury (weakness) which caused the subsequent injuries in respect of which damages were sought.  
  • In Bailey, the Claimant’s weakness was divisible. The pancreatitis and negligent care independently made the Claimant weaker than she otherwise would have been. On the facts, Foskett J was unable to estimate the respective amounts the causal contributions of the pancreatitis and the negligent care made to the weakness. However, had he been able to, then under the principle outlined above, the Defendant’s liability would  be limited to the causal contribution of the negligent care.  
  • By contrast, brain damage and cardiac arrest are surely indivisible injuries. A defendant on this analysis ought to be liable for the totality of the loss which flows from the brain damage and heart attack.  
  • A future issue with which the courts will likely have to grapple is, therefore: can the in/divisibility dichotomy only be applied to a claimant’s ultimate injuries, or can the dichotomy also be applied to the preceding injuries which lead to the ultimate injuries?  

1. For a comprehensive review of the law up until the decision in Thorley v Sandwell & West Birmingham [2021] EWHC 2604 (QB) in October 2021, see Andrew Axon’s guide to material contribution here.

2. Wardlaw v Bonnington Castings [1956] 1 AC 613

3. Bailey v MoD [2008] EWCA Civ 883

4. Bailey v MoD [2007] EWHC 2913 (QB)

5. Thompson v Smith Shiprepairers (North Shields) [1984] QB 405

6. The law here on whether apportionment is available in indivisible injury cases is not a model of clarity. In Williams v The Bermuda Hospitals Board [2016] UKPC 4, the Judicial Committee of the Privy Council approved Prof Sarah Green’s statement that a defendant who contributes to an indivisible injury is liable for the whole, even where there were other contributory causes. Nonetheless, there have been attempts to apportion damages in other cases. For a more detailed consideration of this issue, please see Andrew Axon’s guide to material contribution causation at [57]-[61], [80]-[92], [98].