In September 2019, the UK Supreme Court ruled that Prime Minister Boris Johnson's decision to suspend Parliament for five weeks was unlawful. The government had acted without legal authority, the judges said, and the prorogation was void. Parliament reconvened the next day. It was one of the most dramatic moments in modern British constitutional history, and it turned on a legal process most people had never heard of: judicial review.
Judicial review is the mechanism by which courts can check whether ministers, officials, and public bodies have acted within the law. It is not about whether a decision was right or wrong, but whether it was lawful — whether the decision-maker had the power to do what they did, followed the correct procedures, and acted rationally. Here is how it works, what it can and cannot do, and why it matters.
What Judicial Review Is
Judicial review is a court process that allows individuals, businesses, or campaign groups to challenge decisions made by public authorities. If a court finds that a decision was unlawful, it can quash (cancel) the decision, order the authority to reconsider it, or declare that the authority acted illegally.
Judicial review is not an appeal. An appeal asks whether a decision was wrong on the facts or the law. Judicial review asks whether the decision-maker had the legal power to make the decision in the first place, and whether they exercised that power properly.
The key principle is that public bodies — ministers, councils, regulators, the NHS, the police — must act within the powers given to them by Parliament. If they exceed those powers, act irrationally, or fail to follow proper procedures, the courts can intervene.
The Three Grounds for Judicial Review
The modern framework for judicial review was set out by Lord Diplock in the 1985 case Council of Civil Service Unions v Minister for the Civil Service (the GCHQ case). He identified three grounds on which a decision can be challenged:
1. Illegality
The decision-maker has misunderstood the law, exceeded their legal powers, or failed to take account of something the law requires them to consider. For example, if a minister makes a decision that Parliament's legislation does not authorise, that is illegal.
2. Irrationality
The decision is so unreasonable that no rational decision-maker could have reached it. This is a high bar — courts will not interfere just because they disagree with a decision. The decision must be Wednesbury unreasonable (named after a 1948 case), meaning it is so absurd that no sensible person could have made it.
3. Procedural impropriety
The decision-maker failed to follow the correct procedures, such as consulting those affected, giving reasons for the decision, or allowing people a fair hearing. This includes breaches of natural justice — the principle that decisions should be made fairly and without bias.
A fourth ground, proportionality, is sometimes used in cases involving human rights, asking whether the decision was a proportionate response to the problem.
What Judicial Review Cannot Do
Judicial review is powerful, but it has clear limits.
It cannot overturn Acts of Parliament
The UK does not have a written constitution, and Parliament is sovereign — the supreme legal authority. Courts can interpret laws, but they cannot strike them down. If Parliament passes an Act, the courts must apply it, even if they think it is unjust.
This is the fundamental difference between the UK and countries like the United States, where the Supreme Court can declare laws unconstitutional. In the UK, only Parliament can change the law.
It is not about the merits of a decision
Judicial review does not ask whether a decision was wise, fair, or good policy. It only asks whether it was lawful. A court can find that a minister acted lawfully even if the decision was harsh or unpopular.
It requires standing and timeliness
To bring a judicial review claim, you must have standing — a sufficient interest in the matter. You cannot challenge a decision that does not affect you. And you must act quickly: claims must usually be brought within three months of the decision, and in planning cases, within six weeks.
High-Profile Cases
Judicial review has shaped some of the biggest political moments of recent years.
The prorogation case (2019)
In R (Miller) v The Prime Minister, the Supreme Court ruled that Boris Johnson's decision to suspend Parliament for five weeks in the run-up to the Brexit deadline was unlawful. The court found that the prorogation had the effect of frustrating Parliament's ability to carry out its constitutional functions, and the Prime Minister had not given a lawful reason for it. The decision was unanimous, 11–0.
The ruling was constitutionally significant because it established that the courts could review the use of prerogative powers (powers exercised by ministers without needing Parliament's approval) if they affected the functioning of Parliament.
The Article 50 case (2017)
In R (Miller) v Secretary of State for Exiting the European Union, the Supreme Court ruled that the government could not trigger Article 50 (the process for leaving the EU) without an Act of Parliament. The court held that leaving the EU would change domestic law, and only Parliament could authorise that.
The government had argued it could use prerogative powers, but the court disagreed. Parliament passed the European Union (Notification of Withdrawal) Act 2017, and Article 50 was triggered in March 2017.
The Shamima Begum case (2021)
In Begum v Home Secretary, the Supreme Court ruled that Shamima Begum, who had travelled to Syria to join ISIS as a teenager, could not return to the UK to challenge the removal of her British citizenship. The court accepted that the decision to strip her citizenship was lawful, and that national security concerns outweighed her right to a fair hearing in the UK.
The case illustrated the limits of judicial review: the court did not rule on whether the Home Secretary's decision was right, only that it was within the law.
The Judicial Review and Courts Act 2022
In 2022, the government passed legislation to limit certain types of judicial review, arguing that the system had been abused by campaigners seeking to delay or frustrate government policy.
The Judicial Review and Courts Act 2022 introduced several changes:
- Presumption against quashing orders — Courts are encouraged to suspend quashing orders or make them prospective (applying only from a future date), rather than immediately cancelling unlawful decisions.
- Limits on Cart judicial reviews — These are challenges to decisions by the Upper Tribunal (an appeals body). The Act makes them much harder to bring, after the government argued they were rarely successful and wasted court time.
- Ouster clauses — The Act makes it easier for Parliament to pass laws that exclude judicial review altogether in certain areas, though this remains controversial.
Critics, including the Law Society and human rights groups, argued the reforms weaken accountability and make it harder for citizens to challenge unlawful government action. The government said the changes would reduce frivolous claims and restore balance between the courts and the executive.
Why Judicial Review Matters
Judicial review is one of the few mechanisms that allows ordinary people to hold powerful institutions to account. It ensures that ministers and officials cannot act arbitrarily or exceed their powers, and that decisions are made fairly and in accordance with the law.
It is also a flashpoint in debates about the balance of power between the judiciary and the executive. Governments sometimes complain that judges are overstepping their role and interfering in politics. Judges respond that they are simply enforcing the law that Parliament has made.
The tension is built into the system. Parliament is sovereign, but ministers must act within the law. Judicial review is the mechanism that polices that boundary.
How to Bring a Judicial Review Claim
If you believe a public authority has acted unlawfully, you can apply for judicial review in the High Court (or the Court of Session in Scotland). The process is:
- Pre-action protocol — You must write to the public body explaining why you think the decision is unlawful and giving them a chance to respond or reconsider.
- Permission stage — You apply to the court for permission to bring a judicial review. The court will only grant permission if your claim is arguable. Most claims are refused at this stage.
- Substantive hearing — If permission is granted, the case goes to a full hearing, where a judge will decide whether the decision was unlawful.
- Remedy — If you win, the court can quash the decision, order the body to reconsider it, or make a declaration that the decision was unlawful.
Judicial review is expensive and risky. If you lose, you may have to pay the other side's legal costs, which can run to tens of thousands of pounds. Legal aid is available in some cases, but it is increasingly difficult to obtain.
The Bottom Line
Judicial review is the process by which UK courts can rule that a minister or public body has acted unlawfully, exceeded their powers, or acted irrationally. It does not allow judges to overturn Acts of Parliament — only Parliament can change the law. The grounds for review are illegality, irrationality, and procedural impropriety, and the process is tightly time-limited and requires standing. High-profile cases, including the 2019 prorogation ruling, have shown that judicial review can check even the most powerful figures in government. The Judicial Review and Courts Act 2022 introduced reforms that critics say weaken accountability, while the government argues they prevent abuse of the system. Judicial review is not about whether a decision was right, but whether it was lawful — a crucial distinction in a system where Parliament is sovereign but ministers must still act within the law.