R (on the application of Miller) v Prime Minister [2019] UKSC 41

Key point

  • The Prime Minister, exercising the prerogative of the Crown, cannot prorogue Parliament and prevent it scrutinising the Government without reasonable justification


  • Prorogation is a suspension of Parliament that happens every year to mark the end of the Session (Parliamentary Year)
  • The power to prorogue Parliament is a prerogative power, exercised by the Government on behalf of the Crown
  • In late 2019, three years on from the Brexit referendum, the UK was approaching its deadline to leave the EU, with a minority Conservative government wishing to leave on the deadline, and many other parties wishing to delay it
  • It was widely believed that Parliament would force legislation through, against the will of the Government, to extend the deadline
  • Parliament had at this point been in session for the longest time in four centuries


  • In August 2019 it was announced the Queen, on the advice of the Prime Minister, had given her consent to prorogue Parliament that September.
  • The planned prorogation was for five weeks – unusually long
  • This was widely seen as the Government attempting to prevent having their Brexit agenda blocked by Parliament
  • An application for judicial review was made in the High Court by Gina Miller on the grounds that this violated the principles of parliamentary sovereignty and parliamentary accountability
  • The case was rejected as non-justiciable in the High Court, but in the Scottish Court of Session, a similar bid was successful.
  • To resolve these differences, the case was granted an expedited appeal to the Supreme Court, in which he maximum eleven justices heard the case


  1. Is the lawfulness of PM’s the advice to the Queen justiciable?
  2. If it is, by what standard is its lawfulness to be judged?
  3. By that standard, was it lawful?
  4. If it was not, what remedy should the court grant?

Held (Supreme Court)

  • Appeal allowed; the advice given to the Queen to prorogue Parliament was unlawful, and the prorogation itself is null

Lady Hale and Lord Reed (giving the judgment of the court)

Justiciability of exercise of prerogative

  • In considering prerogative powers, it is necessary to distinguish between two different questions (at [35]):
    1. Whether a prerogative power exists and if so its extent, which is always justiciable
    2. Whether the exercise of that power, within its limits, is open to legal challenge on the recognised grounds of judicial review, which is may or may not be justiciable depending on the nature and subject matter of the particular power being exercised
  • In CCSU, Lord Roskill mentioned at p 418 the dissolution of Parliament as one of a number of powers whose exercise was in his view non-justiciable: [35]
  • The current case concerns the first question: [52]

Limit of prerogative power

  • Two fundamental constitutional principles are relevant to determining the limit of the prerogative power: parliamentary sovereignty and parliamentary accountability (i.e. the accountability of the PM and cabinet to Parliament): [41], [46]
  • Both of these principles would be undermined if Parliament is prorogue for extended periods of time: [42], [48]
  • On account of these two principles, the legal test for the limit is that it will be unlawful if “the prorogation has the effect of frustrating or preventing, without reasonable justification, the ability of Parliament to carry out its constitutional functions”: [50]
  • In this case, as there was no reasonable justification given, especially given the length of the prorogation during a period where a fundamental constitutional change was about to take place, the advice to the Queen was found to be unlawful: [61]

Parliamentary privilege

  • The court is not prevented from granting relief by declaring the advice unlawful due to article 9 of the Bill of Rights
  • Prorogation is not a proceeding of Parliament under Bill of Rights as is imposed upon Parliament from the outside without its participation: [68]
  • It is not a core or essential business of Parliament, it brings that core or essential business to an end: [68]


  • The political and public reaction to this case was huge and divisive. Many on the right saw it as a violation of the separation of powers for the court to decide on political issues, although this argument was given little attention by the court and summarily dismissed at [31] on account of the fact that the courts have always decided cases concerned with politics