The grounds on which a court will quash a public body's decision — illegality, irrationality and procedural impropriety — and the doctrines that have grown around them.
Judicial review polices how public power is exercised, not whether the decision was the right one — a distinction that shapes every ground of challenge. This chapter begins with the nature of review itself and how it differs from an appeal, before working through illegality: acting ultra vires, improper purposes, relevant and irrelevant considerations, and the rules against fettering and unlawfully delegating discretion. It then sets out the irrationality standard and the four-stage proportionality test that displaces it in rights cases, followed by procedural impropriety — bias, predetermination, the fair hearing, the duty to give reasons and the Gunning principles for consultation. The chapter closes with legitimate expectation and material error of fact as further grounds, and the statutory power to refuse relief where the outcome would highly likely have been the same.
