Megan Griffiths and Achas Burin look at the defence of illegality as analysed in the recent Court of Appeal decision, Lewis-Ranwell v G4S Health and others [2024] EWCA Civ 138. The Court of Appeal found by a majority of 2-1 that a claimant acquitted of murder by reason of insanity was not prohibited from bringing a negligence action because, although they had committed a criminal act, they had not been deemed criminally responsible for it and it would be contrary to public policy to debar them.