Ultra vires
The doctrine of ultra vires means a public body acts unlawfully if it goes beyond the powers granted to it by law. It is the constitutional foundation of judicial review, ensuring public bodies act only within their legal authority.
Last reviewed 14 June 2026
Substantive ultra vires covers exceeding the scope of a power, using it for an improper purpose, or taking irrelevant considerations into account; procedural ultra vires covers failing to follow a mandatory statutory procedure.
It maps onto the grounds of judicial review: a decision taken outside legal powers is “illegality” in Lord Diplock's GCHQ classification. Anisminic v Foreign Compensation Commission showed even an ouster clause cannot protect a decision that is a nullity for error of law.
Key cases
- Council of Civil Service Unions v Minister for the Civil Service (GCHQ) [1985] AC 374
- Anisminic Ltd v Foreign Compensation Commission [1969] 2 AC 147
Frequently asked questions
What does ultra vires mean?
Literally “beyond the powers” — a public body acts ultra vires, and unlawfully, when it exceeds the authority granted to it by law.
How does ultra vires relate to judicial review?
It is its foundation: acting beyond legal powers is the “illegality” ground of judicial review (the GCHQ case).