Illegality defence: Ex turpi causa

Lewis-Ranwell v G4S Health Services (UK) Ltd and Others [2026] UKSC 2

The illegality defence has been developed by courts in the UK over many years, and its application depends on the specific facts of each case in which it is pleaded by defendants in civil claims. The Supreme Court recently considered a complex and very tragic case involving a claimant who had been found not guilty of murder by reason of insanity, and who had initiated a claim for damages in a civil action against three organisations which he alleged had been negligent in respect of his treatment while he was experiencing an episode of acute psychosis. The defendants in the civil case were attempting to have the claim struck out on the basis of the defence of illegality (ex turpi causa). The Supreme Court concluded that the illegality defence would apply even where there had been no criminal conviction. That conclusion was an attempt to settle a difficult question involving conflicting moral arguments, but some troubling questions continue to arise. This is an important case that deserves the detailed exposition and analysis below.