In public or administrative law, judicial review is a form of litigation in which the act or omission of a public authority is challenged as being unlawful because

• the authority did not have the requisite power in law.
• the authority failed to follow the proper procedure.
• the authority behaved so irrationally, unfairly, or disproportionally as to invalidate its actions.

“Public authority” in this context usually means a government department (represented by the relevant minister), an agency of the executive (such as HMRC), or a local authority. A preliminary issue in judicial review cases may concern whether the defendant is a public authority susceptible to judicial review or acting as such when doing or failing to do the thing that is said to be unlawful.

A claim for judicial review is not an appeal. It is a substantive action, usually pursued in the Administrative Court (part of the King’s Bench Division of the High Court), in which a claimant seeks one of a number of specific remedies against the relevant public authority. These include:

• a declaration that the act or omission was unlawful
• an order “quashing” a decision (i.e. declaring it of no effect).
• an injunction or order requiring the public authority to act (a mandatory order) or refrain from acting (a prohibiting order) in a particular way.
• in addition to one or more of the above, damages (ie monetary compensation) or restitution.

All claims for judicial review require the court’s permission first. If permission is given, the claim is pursued by the Crown “on the application of” the claimant. Usually we abbreviate this to R (The Claimant) v The Defendant. This practice derives from the origins of judicial review as a way of obtaining prerogative remedies (derived from the Crown). Older judicial review cases were listed as being brought by the Crown against the respondent (not defendant), ex parte (or ex p) the applicant (not claimant).