## Facts

- The United Kingdom’s planned withdrawal from the European Union was scheduled for 31 October 2019.
- On the Prime Minister’s advice, an Order in Council was made to prorogue Parliament between 9–12 September 2019 until 14 October 2019, substantially reducing sitting time during the weeks immediately preceding the planned withdrawal date.
- In proceedings in England and Wales, the High Court Divisional Court held the prorogation advice was not justiciable.
- In proceedings in Scotland, the Inner House of the Court of Session held the matter justiciable and concluded the prorogation was unlawful, void, and of no effect.
- The UK Supreme Court heard the joined appeals before a full bench of 11 justices.

## Issues

1. Whether the Prime Minister’s advice to prorogue Parliament was justiciable in court.
2. If justiciable, what legal limits constrain the prerogative power to advise prorogation.
3. Whether this prorogation had the effect of frustrating or preventing Parliament from carrying out its constitutional functions without reasonable justification.
4. If unlawful, what legal effect followed for the Order in Council and the purported prorogation.

## Decision

- The Supreme Court unanimously held the lawfulness of the Prime Minister’s prorogation advice is justiciable.
- The Court held a prorogation is unlawful if it has the effect of frustrating or preventing, without reasonable justification, Parliament’s ability to perform its constitutional functions as legislator and as supervisor of the executive.
- Applying that standard, the Court held the advice, the Order in Council, and the prorogation were unlawful, void, and of no effect.
- Parliament was not prorogued in law and therefore remained in session.

## Legal Principles

- The existence and scope of prerogative powers are matters of law for judicial determination; courts may review whether such powers were exercised within legal limits.
- Parliamentary sovereignty and parliamentary accountability of the executive are fundamental constitutional principles that limit executive action affecting Parliament’s ability to sit, legislate, and scrutinize government.
- The controlling test focuses on effect: a prorogation is unlawful when it frustrates or prevents Parliament’s constitutional functions without reasonable justification.
- When a purported prorogation exceeds lawful limits, the resulting instruments and acts (including an Order in Council implementing it) are void and of no legal effect.

## Conclusion

The Court held that courts may review prorogation and that an unusually consequential prorogation lacking reasonable justification is unlawful; because this prorogation improperly prevented Parliament from performing its constitutional roles, it was void and Parliament legally remained in session.


R (Miller) v. Prime Minister; Cherry v. Advocate Gen. for Scot., [2019] UKSC 41 (U.K. 2019)