Case Facts
In this case, the claimants challenged the government's assertion that it could use prerogative powers to trigger Article 50 of the Treaty on European Union (TEU) — the formal mechanism by which a Member State notifies its intention to withdraw from the European Union — without prior authorisation by Act of Parliament.
The United Kingdom became a member of the European Economic Community on 1 January 1973. EU law was incorporated into domestic law by the European Communities Act 1972, which had been passed some ten weeks before accession. The European Union Referendum Act 2015 was passed in December 2015, and the referendum held on 23 June 2016 produced a majority in favour of leaving the EU. Following the referendum result, the government announced its intention to trigger Article 50 TEU by the exercise of prerogative powers alone, without seeking prior statutory authorisation from Parliament.
The first respondent, Gina Miller, and the second respondent, dos Santos, brought proceedings challenging this approach. The Divisional Court, in a judgment delivered on 3 November 2016 (reported as [2016] EWHC 2768 (Admin)), upheld the claimants' arguments and held that an Act of Parliament was required before Article 50 notice could be given. The government appealed to the Supreme Court.
Separately, devolution issues arose in proceedings brought in Northern Ireland by Steven Agnew and others and by Raymond McCord. The Northern Ireland High Court dismissed those challenges on 28 October 2016 ([2016] NIQB 85). The Attorney General for Northern Ireland referred four issues to the Supreme Court, which consolidated those references with the main appeal. Related devolution questions also arose in relation to Scotland and Wales, concerning whether the terms of the devolution settlements required Parliament to legislate before formal notice could be given, and whether the consent of the devolved legislatures was legally required.
The case was heard by the Supreme Court on 5, 6, 7 and 8 December 2016, and judgment was delivered on 24 January 2017.
The two constitutional features giving rise to the central issue were: first, ministers' general prerogative power to enter into and terminate international treaties without recourse to Parliament; and second, the established constitutional principle that ministers may not exercise any power — whether prerogative or otherwise — if doing so would result in a change to domestic law unless authorised by statute. The Court emphasised at the outset that it was not concerned with the political wisdom of leaving the EU, the terms of any withdrawal, or the timetable for doing so. Those remained political questions for ministers and Parliament. The Court's role was confined strictly to questions of law.
Held
The Supreme Court dismissed the government's appeal by a majority of 8 to 3. The majority held that the government could not lawfully use prerogative powers alone to trigger Article 50 TEU and that primary legislation — an Act of Parliament — was required before formal notice of withdrawal could be given.
On the devolution question, the Court held unanimously that the devolved legislatures of Scotland, Wales and Northern Ireland were not legally required to consent to the triggering of Article 50. The Sewel Convention — the political convention that Westminster will not normally legislate on devolved matters without the consent of the relevant devolved legislature — is a political convention and is not legally enforceable by the courts.
Following the Supreme Court's judgment, Parliament enacted the European Union (Notification of Withdrawal) Act 2017, which received Royal Assent on 16 March 2017 and authorised the Prime Minister to notify the United Kingdom's intention to withdraw from the EU under Article 50 TEU. The Article 50 notification was ultimately given on 29 March 2017.
Ratio Decidendi
The ratio of the decision rests on the fundamental constitutional principle that the Crown's prerogative powers cannot be used to alter domestic law or to remove rights that Parliament has, by statute, conferred upon individuals resident in the United Kingdom.
The European Communities Act 1972 was held to be of special constitutional character. By enacting it, Parliament had not merely incorporated a body of existing EU law into domestic law: Parliament had created a new and dynamic source of domestic law, one that would change and develop over time as EU law itself changed. EU law thereby became a source of UK domestic legal rights and obligations — rights that individuals could enforce in domestic courts. When the European Communities Act 1972 was passed, Parliament must be taken to have intended that those rights could not be removed by the executive acting alone under prerogative powers, but only by Parliament itself through primary legislation.
The Supreme Court drew a critical distinction between the prerogative power to make and unmake international treaties — which operates at the international level and does not, of itself, change domestic law — and the domestic legal consequences of triggering Article 50. Whilst ministers retain the prerogative to conduct foreign affairs and to enter into or withdraw from treaties at the international level, triggering Article 50 would inevitably and irreversibly set in motion the process by which EU law would cease to be a source of domestic rights. That domestic legal consequence placed the matter beyond the reach of prerogative power and required statutory authorisation.
The majority reasoned that if the executive were permitted to use prerogative power to withdraw from the EU Treaties, it would effectively be using that power to destroy a body of statutory rights that Parliament had conferred — rights that existed as part of domestic law by virtue of the European Communities Act 1972. This would be constitutionally impermissible. It would allow the executive to achieve, through the exercise of prerogative, a result that only Parliament could lawfully bring about.
On the devolution issue, the Court held unanimously that, whilst the Sewel Convention is recognised in statute by s 28(8) Scotland Act 1998, its recognition in statutory form does not convert it into a legally enforceable rule. The convention remains a political constraint upon Parliament's conduct, not a legal one, and the courts have no jurisdiction to enforce it.
Obiter Dicta
The Court reiterated that its decision was confined entirely to the legal question of whether prerogative powers were sufficient authority for triggering Article 50 TEU. The Court expressly declined to express any view on the political merits of Brexit, the desirability of leaving the EU, or the terms on which withdrawal should be negotiated. These observations underline the Court's concern to maintain the boundary between judicial and political decision-making.
The majority also made observations, without deciding the point, about the nature of constitutional statutes. The European Communities Act 1972 was treated as a statute of special constitutional character, consistent with the approach adopted in Thoburn v Sunderland City Council and other appeals [2002] by Laws LJ, under which constitutional statutes cannot be impliedly repealed. Whilst the Court did not need to resolve every aspect of that doctrine, its analysis of the European Communities Act 1972 as a statute that fundamentally altered the relationship between Parliament and the executive is of broader significance for the understanding of constitutional statutes in English law.
The Court's observations on the Sewel Convention are also of general importance. By noting that parliamentary recognition of a convention in statutory form — as in s 28(8) Scotland Act 1998 — does not render the convention legally enforceable, the Court affirmed the orthodox constitutional distinction between legal rules and political conventions, a distinction closely associated with the analysis of A V Dicey and of continuing relevance to the study of constitutional law.