Jus Cogens

Jus cogens norms sit at the top of the hierarchy of international law: they are rules so fundamental that states cannot contract out of them, even by treaty. The UK Supreme Court explained the concept in Belhaj v Straw, holding that the prohibition of torture 'has the status of jus cogens erga omnes. That is to say that it is a peremptory norm of international law which gives rise to obligations owed by each state to all other states and from which no derogation can be justified by any countervailing public interest.' The judgment traces the definition to Article 53 of the Vienna Convention on the Law of Treaties, which describes a peremptory norm as one 'accepted and recognized by the international community of States as a whole as a norm from which no derogation is permitted and which can be modified only by a subsequent norm of general international law having the same character.'

English courts have repeatedly confirmed torture's jus cogens status outside the Supreme Court context too. In a 2025 High Court judgment concerning a good-character assessment for British citizenship, the court observed simply that 'Torture itself is jus cogens and all States have a legal interest in its prohibition' — illustrating how the doctrine now operates as settled law across different areas of practice, from state immunity litigation to nationality decisions.

Jus cogens status does not, however, automatically override every competing legal doctrine. In Belhaj, the Supreme Court held that the House of Lords had been right in Jones v Saudi Arabia to reject 'the argument that torture or some other contravention of a jus cogens cannot attract immunity rationae materiae because it cannot be an official act' — meaning that even a jus cogens violation like torture does not, without more, strip a state of immunity from civil suit in a foreign court, because state immunity is a procedural bar on jurisdiction rather than a rule of substantive law that could conflict with the underlying prohibition.