In a judgment dated 3 November 2016, the High Court ruled that the government of the United Kingdom does not have the power to invoke Article 50 of the Treaty on the Functioning of the European Union (TFEU) to begin the formal process of Britain’s withdrawal from the EU. Instead, an Act of Parliament is required. A summary of the judgment is available here. The government intends to appeal the judgment to the Supreme Court, which, we understand, has indicated that the full panel of eleven judges will hear the case over four days during the week of 5 December 2016.

In July 2016, the Court (Lord Justice Leveson and Mr Justice Cranston) gave directions for the joint management of judicial review claims that challenged the government’s ability to trigger Article 50 of TFEU by means of the royal prerogative (CO/3809/2016 The Queen on the application of Gina Miller v Secretary of State for Exiting the European Union and CO/3281/2016 The Queen on the application of Deir Tozetti Dos Santos v Secretary of State for Exiting the European Union). The joined applications were heard on 13, 17, and 18 October 2016 before the Lord Chief Justice Lord Thomas, the Master of the Rolls Sir Terence Etherton, and Lord Justice Sales (transcripts available here).

The application was intended to settle the question of “whether, as a matter of the constitutional law of the United Kingdom, the Crown – acting through the executive government of the day – is entitled to use its prerogative powers to give notice under Article 50 for the United Kingdom to cease to be a member of the European Union.”1

The leading application was brought by Gina Miller, an investment manager, and was argued by Lord Pannick QC, a cross-bench peer. The applicants’ main argument2 was based on the constitutional principle that the British executive may not change the law of the land by use of royal prerogative – or executive act (as enshrined as early as The Case of Proclamations (1610) 12 Co. Rep. 74). Therefore, owing to the transmission of the European Union treaties and the rights granted therein to domestic law by the European Communities Act 1972 (ECA 1972), the government was barred from invoking Article 50 TFEU and dissolving those domestic rights without the approval of Parliament.

Attorney General Jeremy Wright QC MP, who argued for the government, relied on the equally settled constitutional principle that the executive has prerogative power in the field of making and breaking treaties on the international plane; and that no legislation, not least the ECA 1972 itself, nor the European Union Referendum Act 2015, had done away with the executive’s power unilaterally to withdraw the U.K. from the EU treaties as constitutional custom would ordinarily allow.3

The applicants and various interveners made other arguments in the alternative to the main position. However, the Court did not feel it necessary to consider these arguments, and settled the issue on the primary question of whether the ECA 1972 had restricted prerogative power. The Court had held that, by its nature, the ECA 1972 is a part of the constitutional framework of the U.K., and should be interpreted in that light.4 That being so, at the crux of the Court’s judgment, it found that:

"Parliament having taken the major step of switching on the direct effect of EU law in the national legal systems by passing the ECA 1972 as primary legislation, it is not plausible to suppose that it intended that the Crown should be able by its own unilateral action under its prerogative powers to switch it off again."5

Its decision follows, and discussed, previous jurisprudence on the use of prerogative powers in Attorney General v De Keyser’s Royal Hotel [1920] AC 508, R v Secretary of State for the Home Department, ex p. Fire Brigades Union [1995] 2 AC 513 and Laker Airways Ltd v Department of Trade [1977] 643 (CA), that primary legislation may impliedly abrogate Crown prerogative, including in the sphere of treaty making. The Court particularly distinguished R v Secretary of State for Foreign and Commonwealth Affairs, ex p. Rees-Mogg [1994] QB 552 (DC), a previous holding that the ECA 1972 did not circumscribe the executive’s ability to use prerogative power in order to join the U.K. to further EU treaties which did not have direct domestic legal effects. The Court found that:

"In the very different context of the present case, the question is whether the Crown has power under its prerogative to withdraw from the relevant EU Treaties where such withdrawal will, on the [government]’s argument, have a major effect on the content of domestic law. It is clear that the court in ex p Rees Mogg did not touch on that question."6

The first-instance decision, if upheld by the Supreme Court, suggests that a vote in Parliament will be required before the government may invoke Article 50 TFEU. This could potentially deal a blow to the timetable recently set out by Prime Minister Theresa May for formal exit procedures to begin by the end of March 2017, and perhaps even affect the prospect of the U.K.’s leaving the EU at all.