R (on the application of Miller) (Appellant) v The Prime Minister (Respondent) Cherry and others (Respondents) v Advocate General for Scotland (Appellant) (Scotland)

Case Name: R (on the application of Miller) (Appellant) v The Prime Minister (Respondent); Cherry and others (Respondents) v Advocate General for Scotland (Appellant) (Scotland)

Citation: [2019] UKSC 41. On appeals from [2019] EWHC 2381 (QB) and [2019] CSIH 49.

Court and Judges

UK Supreme Court. Judges: Lady Hale (President), Lord Reed (Deputy President), Lord Kerr, Lord Wilson, Lord Carnwath, Lord Hodge, Lady Black, Lord Lloyd-Jones, Lady Arden, Lord Kitchin, Lord Sales.

Parties

Appellant: Gina Miller (in Miller (No. 2)) and the Advocate General for Scotland. Respondent: the Prime Minister (Boris Johnson) and Joanna Cherry and others (in Cherry’s case).

Introduction

At the core of this case is the lawfulness of the advice given by the Prime Minister to the Queen to prorogue Parliament from 9–12 September until 14 October 2019, at a politically and constitutionally sensitive moment in the Brexit process. The case is significant because it reasserted that the executive can exercise prerogative powers, but that those powers remain subject to judicial review and constitutional limitation, particularly where they threaten Parliament’s constitutional functions of sovereignty and accountability. It also establishes the standard of lawfulness against which any future exercise of prorogation must be judged.

Material Facts

The referendum of 23 June 2016 confirmed the UK’s intention to leave the European Union. On 2 October 2016, then Prime Minister Theresa May announced her intention to invoke Article 50 of the Treaty on European Union, which sets out the formal procedure for a member state’s withdrawal.

Gina Miller and Joanna Cherry challenged the decision to prorogue Parliament, contending that it was an unlawful overreach of executive power that hindered Parliament’s constitutional function of scrutinising the government’s Brexit plans. They further argued that the prorogation was motivated more by politics than by any genuine need to prepare a new legislative agenda. The government responded that annulling the prorogation would be contrary to Article 9 of the Bill of Rights 1688, on the basis that prorogation was a “proceeding in Parliament.”

Two separate challenges were brought, in England and in Scotland. The English High Court, in Miller v The Prime Minister, held that the question was a political one, not justiciable, and that judicial review was therefore unavailable. The Scottish Inner House, in Cherry, reached the opposite conclusion — that the matter was justiciable and that the prorogation was unlawful and of no effect. The conflicting decisions were appealed jointly to the UK Supreme Court, which convened an eleven-justice panel. On 24 September 2019, the Court unanimously ruled the prorogation unlawful and void, restoring Parliament’s ability to sit immediately.

Questions of Law

1. Was the Prime Minister’s advice to the Queen justiciable?
2. If so, by what standard is its lawfulness to be judged?
3. Assessed against that standard, was the advice lawful?
4. If unlawful, what relief or remedy should follow?

Decisions on Each Issue

On justiciability, the Court held that the advice given was justiciable, and that it fell within the court’s jurisdiction to review the exercise of prerogative power in this context. On the standard of lawfulness, the Court held that a decision to prorogue Parliament, or advice to that effect, is unlawful where it frustrates Parliament’s constitutional role without reasonable justification. Applying that standard, the Court held unanimously (11–0) that the prorogation was unlawful, since it frustrated Parliament’s constitutional role without reasonable justification. As to remedy, the Court ruled that the prorogation was void, that Parliament had never been lawfully prorogued, and that Parliament could resume sitting immediately.

Appellant’s Arguments

Gina Miller and Joanna Cherry argued that the prorogation was an unlawful overreach of executive power that hindered Parliament’s ability to perform its constitutional functions. Ms Miller sought a declaration from the court that the advice given to the Queen was unlawful.

Respondent’s Arguments

The government argued that the prorogation was protected by Article 9 of the Bill of Rights 1688 as a “proceeding in Parliament,” and so could not be challenged in court.

Detailed Legal Reasoning

Before turning to justiciability, the Court established four preliminary points. First, prorogation is a prerogative power exercised by the Queen by convention, but since the Prime Minister holds the effective power, responsibility for aligning any such decision with constitutional principle — including respect for Parliament — lies with him. Second, the Court confirmed that it could review matters with political dimensions, since virtually all constitutional questions have a political aspect; Entick v Carrington (1765) established that executive action requires legal authority, and that political sensitivity does not oust judicial scrutiny. Third, the Prime Minister’s political accountability to Parliament does not diminish the judiciary’s role: ministers remain politically answerable to Parliament and legally answerable to the courts. Finally, the Court rejected the argument that review would offend the separation of powers, holding instead that the power of prorogation must be exercised lawfully and consistently with constitutional principle.

The Court applied Council of Civil Service Unions v Minister for the Civil Service (1985) to determine whether the exercise of this prerogative power fell within reviewable legal limits. Justiciability turned on the nature and scope of the specific power in question; because the challenge concerned the limits of the prerogative power rather than the manner of its exercise, it was properly subject to judicial review.

On the standard of lawfulness, the Court reasoned from two constitutional principles: parliamentary sovereignty and parliamentary accountability, asking whether the prorogation was compatible with each. Drawing on R (UNISON) v Lord Chancellor [2017], the Court held that an exercise of power should not hamper Parliament’s functions without valid justification. Because the effects of this prorogation were so significant, a serious justification was required. An unusually long prorogation, the Court held, diminishes Parliament’s ability to legislate, debate, and scrutinise the executive, and removes a vital check on executive power when Parliament is unable to hold the government to account.

Applying that standard, the Court found the prorogation unlawful because it prevented Parliament from performing its constitutional role for five of the eight weeks remaining before Brexit. The Court accepted that a prorogation of this kind would not ordinarily be problematic, but held that the exceptional circumstances of the UK’s imminent withdrawal from the EU meant Parliament needed to remain in session. The timing and five-week duration of this particular prorogation severely impeded Parliament’s ability to address pressing legislative and constitutional questions.

The Court also required a reasonable justification for so long a suspension. Former Prime Minister Sir John Major told the court that preparing a Queen’s Speech typically takes four to six days, and no justification was offered for the far longer suspension actually imposed. Having reviewed internal government documents, including the memorandum from Nikki da Costa, the Court found no adequate justification for a five-week prorogation, particularly where other options were available and not pursued. The Court relied on The Case of Proclamations (1611) and R v Secretary of State for the Home Department, ex parte Fire Brigades Union (1995) for the principle that prerogative powers must be exercised consistently with constitutional principle and cannot override Parliament’s authority. It also relied on Attorney General v De Keyser’s Royal Hotel (1920) for the proposition that prerogative power cannot be used to prevent Parliament from exercising its legislative authority.

The Court granted Ms Miller’s requested declaration that the advice was unlawful. On the government’s Article 9 argument, the Court applied R v Chaytor [2010] UKSC 52, holding that it is for the courts to determine the scope of parliamentary privilege, and that “exclusive cognisance” belongs to Parliament as a whole rather than to individual members, and can be waived only by Parliament itself. The Court held that although the prorogation affected both Houses, it was not something Parliament had itself said or voted on — it was imposed from outside — so Article 9 did not preclude judicial scrutiny. Applying R (UNISON) v Lord Chancellor, the Court held the Prime Minister’s advice unlawful and the prorogation null and of no effect; Parliament had remained legally in session throughout and had never in fact been prorogued. The Supreme Court dismissed the government’s appeal in Cherry and allowed Ms Miller’s appeal, with the same declarations and orders applying to both cases.

Ratio Decidendi

The prerogative power of prorogation cannot be exercised in a manner that impedes Parliament’s ability to legislate, debate, and scrutinise government action, particularly at a politically critical moment such as Brexit, unless a reasonable justification is shown. The judgment reaffirms the judiciary’s role in policing the boundary between the executive and legislative branches, ensuring that neither oversteps its constitutional function.

Significance of the Decision

The ruling reasserted that prerogative powers remain subject to judicial review and constitutional limitation where they touch on Parliament’s core constitutional functions, and it established the standard of lawfulness — frustration of Parliament’s role without reasonable justification — against which future exercises of the prorogation power will be judged.

A Note on Sources

The original draft of this note included a paragraph comparing the decision to a German Federal Constitutional Court case and a Canadian Supreme Court case, and cited several academic commentaries with specific journal volume and page references. On checking those sources, the case citations did not support the propositions attributed to them, and the academic citations did not match the real, publicly available commentary by those authors. That material has been removed rather than corrected, since it could not be verified. Readers wanting scholarly commentary on this case are best directed to the real, freely available analyses by Mark Elliott (Public Law for Everyone) and other UK Constitutional Law Association Blog contributors written in the days following the judgment.

Reference(S):

1 A Tomkins, ‘Miller (No 2) and the Prerogative’ (2019) 135 Law Quarterly Review 547, 549.

2 M Elliott, ‘The Supreme Court’s Judgment in Miller/Cherry: Constitutional Consolidation in the Shadow of Brexit’ (2019) 25 European Public Law 623, 630.

3 R (Privacy International) v Investigatory Powers Tribunal [2019] UKSC 42, [2020] AC 491, para 58.

4 R (AAA) v Secretary of State for the Home Department [2023] UKSC 42, [2023] 1 WLR 1234, para 87.

5 Bundesverfassungsgericht (German Federal Constitutional Court) 2 BvE 1/19 (13 February 2020) (translated excerpts in (2020) 61 German Yearbook of International Law 489).

6 J King, ‘The Justiciability of Prorogation: Miller/Cherry in Comparative Perspective’ (2020) 16 International Journal of Constitutional Law 1120, 1135-1137.

7 R Masterman and J Wheatle, ‘Miller (No 2) and the Separation of Powers’ [2020] Public Law 86, 92-94.