Unlike most defences, illegality is a complete answer: if it succeeds, the claim fails altogether, however careless the defendant. This chapter begins with what the defence is and the effect it has on a claim, then sets out the central question the court asks and the three-factor policy and proportionality framework that now governs the answer. It works through what the defendant must establish — including who bears the burden, how serious the claimant's conduct must be, and the connection required between that conduct and the loss — before examining the proportionality assessment and how illegality differs from the partial defence of contributory negligence. It closes with how the defence operates on the facts: whether a conviction is needed, when losses separable from the claimant's wrongdoing remain recoverable, and whether the defendant's own illegality matters.
