Divisible or indivisible injury? It might be immaterial
The court held that the doctrine of material contribution can apply as much to indivisible injuries as it can to those that are divisible.
A new judgment from the Court of Appeal in Holmes v Poeton Holding Ltd  EWCA Civ 1377 on this difficult area of law provides further guidance which is unlikely to be welcomed by defendants.
The circumstances in which the established “but for” causation test is modified have long been controversial.
Legal practitioners, experts, and courts have wrestled with the applicability of material contribution where the traditional test is inappropriate.
In Thorley v Sandwell & West Birmingham NHS Trust  EWHC 2604, Justice Soole described the law on material contribution as “ripe for authoritative review” which is hardly surprising given some of the prior inconsistent rulings.
Since Bonnington Castings Ltd v Wardlaw , which introduced material contribution as an alternative to establishing causation on the “but for” test, it has been a matter of contention for litigating parties.
Practitioners will be a familiar with a number of high profile cases, not least Bailey v The Ministry of Defence & Anor  1 WLR 1052 in which it was said that the doctrine only applied in cases where medical science cannot establish causation on the “but for” test; Ministry of Defence v AB & others  EWCA Civ 1317 in which it was held that the principle only applies where the condition is “divisible”; and Williams v Bermuda  UKPC 4 in which Lord Toulson said it was “trite law” that a defendant causing or contributing to an “indivisible” injury will be held fully liable for it. In John v Central Manchester and Manchester Childrens’ University Hospitals NHS Foundation Trust  EWHC 407 QB it was held that there must be a cumulative effect of the causative agent and the severity of the disease must increase with exposure.
Whether an injury is divisible or indivisible and, accordingly, whether material contribution could apply is also controversial. The general consensus is that an injury which is made more severe by exposure to the noxious/negligent agent is “divisible” (for example asbestosis or industrial deafness in which severity correlates with exposure) whilst those injuries which are not worsened by exposure are “indivisible” (for instance cancer or mesothelioma).
More recent cases which have grappled with the doctrine and added to the confusion include Davies v Frimley Health NHS Foundation  EWHC 169 in which the court appeared to accept that material contribution only applied to divisible injuries. In Thorley the judge considered himself bound by AB and it was held that material contribution has no application to a case where there is indivisible injury an one tortfeasor.
Defendants have subsequently often defended material contribution claims on the basis that the injury is indivisible and ensuring that the claimant must satisfy the more onerous “but for” test.
However, the Court of Appeal’s recent decision in Holmes v Poeton Holding Ltd  may change the landscape (https://www.bailii.org/ew/cases/EWCA/Civ/2023/1377.html). The claim related to whether the claimant’s Parkinson’s disease had been caused, or materially contributed to, by exposure to noxious agents in his employment.
In his judgment LJ Stuart-Smith weighed up much of the previous case law and disagreed with much of it. Whilst maintaining the accepted definitions of a “divisible” and “indivisible” injury, he considered previous decisions, notably Bonnington, had miscommunicated the difference and the error had been carried forward.
Whilst the claim ultimately failed, the court held that the doctrine of material contribution can apply as much to indivisible injuries as it can to those that are divisible.
The judgment is unlikely to be welcomed by defendants but will provide some long-awaited certainty and, it remains, that the doctrine is a modified version of the traditional “but for” test and will have limited applicability.