This article explores the approach of the appellate courts in England and Wales to cases where an offender is properly convicted of a criminal offence under law as understood at the time of their conviction, but that law is later reinterpreted such that they might not have been convicted under the reinterpreted law. This may be because the scope of a defence has changed, or the elements of the offence that the prosecution must prove have altered, through reinterpretation of the common law or a statute by the courts. In such scenarios, any appeal is governed by the same requirements as all other appeals. To succeed in their appeal, the appellant must secure leave to appeal, and if they are granted leave, must show that their conviction is unsafe.