Supreme Court · Unanimous, eleven justices; joint judgment of Lady Hale and Lord Reed
Facts
In August 2019 the Prime Minister advised the Queen to prorogue Parliament from a date in the second week of September until 14 October 2019, and an Order in Council gave effect to that advice. The period was nearly five weeks and fell a few weeks before the date of the United Kingdom leaving the European Union. The claimants argued that the advice was given to prevent Parliament from scrutinising the government and acting on the departure.
History
In the English proceedings, the Divisional Court held that the matter was not justiciable. In the Scottish proceedings, the Inner House of the Court of Session held that the matter was justiciable and that the advice was unlawful because it had been given for the improper purpose of preventing Parliament from scrutinising the government. Both decisions were appealed to the Supreme Court.
Issue
Whether the lawfulness of the advice to prorogue Parliament, and the prorogation that followed, was justiciable, and if so by what standard it should be tested, and whether the advice was unlawful and with what effect.
Held
The appeal in the English case was allowed and the appeal in the Scottish case was dismissed. The advice was justiciable and unlawful, the prorogation was void and of no effect, and Parliament had not been prorogued.
Ratio
- The courts can decide whether a prerogative power exists and what its limits are, and these limits are justiciable; the use of the power to prorogue Parliament is subject to the limits imposed by the fundamental constitutional principles of parliamentary sovereignty and parliamentary accountability.
- A decision to prorogue Parliament, or advice to do so, will be unlawful if it has the effect of frustrating or preventing, without reasonable justification, the ability of Parliament to carry out its constitutional functions as a legislature and as the body responsible for the supervision of the executive.
- No justification had been offered for the five week prorogation, so the advice was unlawful and the Order in Council and the prorogation were void, as though the prorogation had never taken place.
The judgments
Lady Hale and Lord Reed (lead)
In a joint judgment on behalf of all the justices, they held that the case concerned the legal limits of the power, which the courts can decide, that the length of the prorogation would have a serious effect on the functions of Parliament during a period of exceptional importance, and that no reasonable justification had been given for it.
Key reasoning
- The court relied on the long line of authority that the courts decide the extent of prerogative powers, from the Case of Proclamations and Entick v Carrington to the decisions on the Council of Civil Service Unions and the Fire Brigades Union.
- Two constitutional principles limit the power to prorogue: Parliament as the legislature is sovereign, and the government is accountable to Parliament, and a prorogation that prevents Parliament from performing those functions undermines them.
- The court looked at the effect of the prorogation and not at the motive, and asked whether there was a reasonable justification, which meant that it was not necessary to decide whether the advice was given for an improper purpose.
Where it fits in the module
In the study of the Crown and the royal prerogative, the case restates the relationship between the courts and the political constitution. It tests the extent to which the courts will use fundamental principles to limit a power that had been regarded as political, and shows the relationship between parliamentary sovereignty and the rule of law.
Criticisms
- The new test of frustrating Parliament without reasonable justification is imprecise, and it is unclear what counts as a reasonable justification or how long a prorogation may be.
- The court was drawing on principles it described as fundamental in a way that could be said to create new constitutional law in place of applying settled authority, which raises concerns about the legitimacy of judicial decisions on political questions.
- The finding that the prorogation was void as though it had never taken place is dramatic, and raises questions about the effect on the proceedings of Parliament and on the position of the Crown in giving effect to advice.
- The case was resolved in the heat of a political crisis, and critics argue that the boundary between legal and political accountability should be left to Parliament and not set by the judiciary.
Written with AI (claude-sonnet-5.5 (Claude Code writer)) on 1 November 2026, reviewed for errors by a second model (claude-sonnet-5.5 (Claude Code checker)). Read the case itself on Find Case Law. Spotted an error? Tell us.