The Crown cannot give notice under Article 50 without the approval of Parliament, the High Court has held.
And while the decision will be appealed, prominent constitutional law specialist Professor Michael Zander QC believes it would be “extremely surprising” if the Supreme Court overturned the ruling.
The historic decision, in Santos and Miller v Secretary of State for Exiting the EU [2016] EWHC 2768 (Admin), means MPs must be given a vote on whether the UK can start the process of leaving the EU.
David Greene, NLJ consultant editor and partner at Edwin Coe, who acted for the claimants, said: “[This is] a victory for Parliamentary democracy.
“I now hope that everyone will respect the court’s decision.”
Greene said the Supreme Court would hear the appeal in early December, with a result expected in December or early January.
Professor Zander said: “The Divisional Court’s unanimous decision is very clear and very strong.
“It completely rejects the arguments advanced by the Attorney General for the government. Triggering Article 50 to start withdrawal from the EU requires Parliamentary approval not in the form of a vote but in the form of a statute.
“It would be extremely surprising if the Supreme Court reversed the decision. The government’s Brexit plans have suffered a major reverse.”
The issue before the court was whether the government to trigger Art 50 by exercise of the Crown’s prerogative powers and without reference to Parliament. The court noted that it has been established for hundreds of years that the Crown (the government) cannot exercise prerogative powers to override legislation enacted by Parliament.
Giving judgment, Lord Thomas, Sir Terence Etherton and Lord Justice Sales explained that the general rule that international relations and treaties fall within the scope of the Crown’s prerogative powers exists precisely because these matters have no effect on domestic law. Giving notice under Art 50 would change domestic law. The government contended that Parliament must have intended when it enacted the European Communities Act 1972 that the Crown would retain its prerogative powers to leave the Community Treaties and therefore the EU.
The court ruled, however, that nothing in the 1972 Act supported the government’s argument. It held that the government’s argument was contrary both to the language used by Parliament in the 1972 Act and to the fundamental constitutional principles of the sovereignty of Parliament and the absence of any entitlement on the part of the Crown to change domestic law by exercise of its prerogative powers.
Lord Thomas, Sir Terence Etherton and Lord Justice Sales said: “Absent such authority from the [1972 Act] or the other statutes, the Crown cannot through the exercise of its prerogative powers alter the domestic law of the UK and modify rights acquired in domestic law under the [1972 Act] or the other legal effects of that Act.”
Their judgment does not comment on the effect of the Act of Union of 1707 or the Northern Ireland Act 1998.
A government spokesperson said: “The government is disappointed by the court’s decision… the government is determined to respect the result of the referendum.
“We will appeal this judgment.”
Jacqueline Kendal, senior associate at Rosling King, said: “Parliament needs to vote in favour of doing so before Article 50 is invoked, thereby allowing the UK to leave the EU.
“This is going to be very difficult as the majority of MPs believe that remaining in the EU is in the UK’s best interests, although some have indicated that despite their privately held beliefs, they will follow the decision of the referendum. Certainly, putting the matter to a Parliamentary vote will heighten tensions.
“This is possibly the most important constitutional case of the century.”
