The common law defence of criminality (ex turpi causa) does not operate in European Convention law so as to bar a claim under the Human Rights Act 1998. However, the core of the defence is not criminality but causation which will be relevant to such a claim. The court must ask this question: is what the claimant has done the cause of the harm he suffered, even if there was wrongful conduct by the defendant without which the harm would not have occurred? (Al Hassan-Daniel v Revenue and Customs Commissioner