The claimant joined the defendant company as an apprentice and worked for 15 years on the shop floor where, as part of his duties, he cleaned or degreased engineering components with an organic solvent( TCE). In 1997 he was promoted to a managerial role and his work on the shop floor became more limited. In 2014 he was diagnosed with Parkinson’s disease and he continued to work until 2020 when ill-health forced him to retire early. He brought a claim for damages from the company contending it had acted in breach of its common law and statutory duty in the period from 1982 to 1997 by exposing him to unsafe levels of TCE in the course of his employment. The judge found in the claimant’s favour on both issues leading him to conclude that the company was liable to the claimant for all the consequences of his having contracted Parkinson’s disease—effectively a claim for 100% damages. The company appealed on the issue of causation on the grounds that the judge adopted the wrong legal test for establishing causation of an “indivisible disease”, namely a disease the severity of which, once contracted, would not be influenced by the total amount of the agent which caused it, by concluding that it was sufficient for the claimant to demonstrate that the defendant's breach of duty had made a material contribution to his injury regardless of whether, but for the tort, the injury would have occurred in any event.

On the appeal—