This article considers the rule that a claimant who has been wronged will be denied recovery where the damage flowed from a sanction imposed as a result of their own illegal acts such that compensating the claimant would divert a sanction intended to be imposed on the claimant to the defendant. The article has two purposes. The first aim is to provide a counterweight to the overwhelming body of academic literature critical of Gray v Thames Trains Ltd. in which the House of Lords, in applying the illegality bar found it unnecessary to examine the purpose of the criminal sanction against the claimant, preferring to treat its existence as sufficient to lead to a denial of recovery. The article argues that academic support for adoption of an alternative test of “significant personal responsibility” rests on precarious grounds, depending, as it does, on the “unsatisfactory state of law” and “different policies” arguments. This article reconceptualises the rule in Gray and systematically examines the role played by the theme of consistency between the civil law and criminal law in judicial decision-making. The second aim is to evaluate Gray in light of Patel v Mirza. The article critiques the Supreme Court's inconsistent treatment of deterrence in Henderson v Dorset University NHS Foundation Trust and Stoffel v Grondona, and argues that the way the court in Henderson conceptualised the relationship between Gray and Patel discloses an approach which is more closely aligned with that adopted by the minority in Patel.

The illegality defence is an important element of private law, but its operation has been unpredictable. In Patel v Mirza, the Supreme Court opted for a flexible approach, which does not increase predictability. This approach was recently confirmed in Henderson v Dorset Healthcare University NHS Foundation Trust and Stoffel & Co v Grondona. I propose a principle to guide the application of the illegality defence in tort: namely, the claim fails for illegality if the claimant's harm is the ordinary result of the claimant's wrongdoing. It is argued that the guiding principle: (i) substantially explains the case law; (ii) is normatively defensible; and (iii) makes the defence much more predictable.