The High Court of England & Wales has ruled in R (Miller) v Secretary of State for Exiting the EU [2016] EWHC 2766 (Admin) that only UK Parliament has the authority to give notice under Article 50 of the Treaty on the European Union (“EU”) to leave the EU.

Usually the Divisional Court comprises two High Court trial judges. Being a matter of great constitutional importance, the Court comprised Lord Thomas of Cwmgiedd LCJ (who is the head of the judiciary and President of the Courts of England and Wales), Sir Terence Etherton MR (is the second most senior judge in England and Wales) and Sales LJ. Their unanimous decision turned on the fundamental principle of constitutional law that the Crown (acting through the Government of the day) in the exercise of its prerogative powers cannot overturn an Act of Parliament. It was common ground between the parties that any decision to give notice under Article 50 would inevitably have the effect of changing domestic law. On that basis, the Court concluded that the decision to trigger Article 50 must be made by Parliament, even though it relates to an international treaty.

From a legal perspective, the judgment upholds the sovereignty of Parliament and reinforces the limits of the Crown’s prerogative powers. It is also significant that the ruling was made by the UK’s two most senior judges. It represents a strong endorsement of the doctrine of the separation of powers in the UK context.

While the case will now be heard by the UK Supreme Court on appeal, “leap-frogging” the Court of Appeal, the High Court’s ruling is likely to have immediate political implications.

Background to the judgment

In 1972, UK Parliament passed the European Communities Act 1972 to allow the UK to join what were then called the European Communities, including the European Economic Community. The European Communities became the EU.

Under the European Union Referendum Act 2015, a non-binding referendum was held on 23 June 2016 on the question of whether the UK should leave or remain in the EU. The result of the referendum was that a small majority of voters opted to leave the EU. Indeed, only 51.89% of those who voted, being 72.21% of registered voters (i.e. 37.5% of registered voters) voted to leave; put another way, 62.5% of voters did not vote to leave.

The process for withdrawal from the EU requires the UK to give notice of its decision to the European Council under Article 50 of the Treaty of the EU. Thereafter, the UK would have two years to negotiate and conclude an agreement regarding the arrangements for its withdrawal.

Traditionally, matters relating to international treaties have fallen within the Crown’s prerogative powers (as exercised by the Secretary of State, who is the respondent in this case). As a result, it was assumed by many that the Government could invoke Article 50 without the involvement of Parliament. This assumption was challenged by the various claimants and interested parties in this case, whose rights and interests would be affected in different ways by the UK’s withdrawal from the EU.

Prerogative powers - The limits of executive authority

Unlike in other jurisdictions, the UK Government’s executive powers are not delineated by a single written document. The Court clarified that the Crown only has such powers that are recognised by common law and are not already covered by statute. In this context, the judgment confirms that Parliament has the supreme power to make laws on any subject, which will override any decision of the Government.

While the Court acknowledged that the conduct of international relations, and the making and unmaking of treaties on behalf of the UK, was a matter that would ordinarily be within the Government’s executive authority, it ruled that this power is subordinate to any Acts of Parliament and could not be used to effect change to such laws. The Court accepted that treaties can have certain indirect “interpretive effects” in relation to domestic law but cannot vary or dispense with the rights and obligations conferred by the common law or statute.

No implied right of the Government to withdraw from the EU

The parties accepted that giving notice under Article 50 of the Treaty on the EU was irrevocable and must be made on an unconditional basis. It was also undisputed that invoking Article 50 would cause changes to UK domestic law. In this context, Counsel for the Secretary of State submitted that the European Communities Act 1972 does not expressly remove the Crown’s power to withdraw from the treaties giving rise to the EU and must be interpreted to the effect that the Government retained such power.

The Court rejected this submission. It concluded that nothing in the European Communities Act 1972 supported the view that the Government holds the power to withdraw from the EU and cause consequential amendments to domestic law. The Court refused to “imply” this power from the Act.

The stalemate continues, turbulence ahead

While the judgment will now be heard by the Supreme Court on appeal, the High Court’s ruling is likely to have significant political implications for the UK. At this stage, it remains unclear whether Parliament will vote to give notice under Article 50. It also raises the prospect that the Government may call an early election or use the situation to negotiate an alternative deal from Brussels. In the meantime, the stalemate over Brexit is likely to continue. This will inevitably cause disruption to the usual business of the Government and Parliament. One certain consequence for UK law is that few other reforms will be passed until it is clear whether Brexit will happen.