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R (Miller) v. The Prime Minister [2020]

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This case was seen by the Supreme Court. The Government’s 2019 prorogation was deemed unlawful as in the particular circumstances it frustrated Parliament’s ability to work in the way they are constitutionally required.

Acting on the advice of the Prime Minister, Her Majesty the Queen prorogued Parliament for a period of 5 weeks. Whilst short prorogations of under 10 days are established practice, this prorogation would have been exceptionally long lasting 34 days. Many thought that, despite the official government line, the real reason for the extended prorogation was to prevent proper scrutiny of the Withdrawal Agreement, prompting appeals against the prorogation both in the Scottish Court of Session and the English High Court, both reaching different decisions on matters of justiciability. The case was then awarded an expedited appeal to the Supreme Court, where the maximum eleven justices heard the case.

The case covers four main issues:

(1) Is the question of whether the Prime Minister’s advice to Her Majesty was lawful justiciable in a court of law?

(2) If yes, by what standard is this lawfulness to be judged?

(3) In the present case, by this standard, was it lawful?

(4) If no, what remedy should be granted by the court?

The Court held that the decision to prorogue Parliament was indeed justiciable, as prerogative powers are limited by statute and common law. A prorogation would be found to be unlawful if it had the effect of frustrating or preventing Parliament from carrying out its constitutional requirements, without reasonable justification.

In the present case, the court held there was no justification, let alone a reasonable one, and found the Prime Minister’s advice to the Queen to be unlawful. This had the effect of making it so the prorogation was null and void, and so had never happened; that parliament had never been prorogued.

This judgment offered significant clarification and development of several key constitutional principles, ever-changing in the flexible British constitution, including the doctrines of Parliamentary Sovereignty, Parliamentary Accountability, and the Separation of Powers.

Appellate History

  • Inner House of the Court of Session [2019]: Decision Approved
  • High Court of Justice [2019]: Decision Rejected


  • Prerogative Powers
  • Separation of Powers
  • Parliamentary Sovereignty
  • Parliamentary Accountability

Submission Details

Reviewed by Louis Stripp

Submitted by Iona Lindsay

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  • R (Miller) v Secretary of State for Exiting the European Union [2017] UKSC 5
  • R (Jackson) v Attorney­ General [2005] UKHL 56
  • Thoburn v Sunderland City Council [2002] EWHC 195
  • R (UNISON) v Lord Chancellor [2017] UKSC 51
  • Case of Proclamations (1611) 12 Co Rep 74
Updated on July 13, 2023

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