Theresa May and BrexitGETTY

Ms May’s intention to start the process of leaving the EU by March 2017 has been deemed unlawful

In one of the most important constitutional cases in generations, a QC argued the prime minister had no legal power to trigger Article 50 of the Lisbon Treaty to leave the European Union without the prior authorisation of Parliament.

Mrs May announced at the Conservative Party conference that she intends doing so by the end of March 2017.

Lord Pannick QC attacked her decision on behalf of Gina Miller, an investment fund manager living in London who voted Remain in the EU referendum on June 23.

Miller is the lead claimant in a historic legal action with several other applicants, including the so-called “People’s Challenge” which has the backing of thousands of supporters, all seeking to overturn Mrs May’s decision in judicial preview proceedings at the Royal Courts of Justice in London.

Lord Pannick told three judges in a packed courtroom, with other members of the public listening in two overspill courtrooms, that the case “raises an issue of fundamental constitutional importance concerning the limits of the power of the Executive”.


Lord Chief Justice Thomas, Sir Terence Etherton and Lord Justice Sales are all hearing the challenge

The QC argued Mrs May could not use royal prerogative powers to remove rights established by the European Communities Act 1972, which made EU law part of UK law, as it was for Parliament to decide whether or not to maintain those statutory rights.

He said the question of the legal limits on Executive power “arises in the context of one of the most important of our statutes which is the source of so much of the law of the land.”

Lord Pannick said the case was not concerned with the “political wisdom” of the country withdrawing from the EU and it was wrong to suggest that the legal challenge was “merely camouflage” for those who wanted to remain.

Ms Miller was entitled to say that “if we are to leave the EU then the steps to be taken which will deprive her of her rights under the 1972 Act, and other legislation, must be done in a lawful manner”.

She accepted that her challenge could only succeed “if we can satisfy the court that the defendant has no power to notify under royal prerogative powers”.

Lord Pannick argued it was “entirely a matter for Parliament” to enact legislation authorising withdrawal from the EU, possibly imposing limits on the powers of the Government with regard to notification of Article 50, perhaps requiring ministers to report back to Parliament or defining terms.

The sovereignty of Parliament meant that what Parliament did “is entirely a matter for Parliament”.

Government lawyers are arguing that if Ms Miller and her supporters’ legal challenge succeeds, the Government “could not give effect to the will and decision of the people, as clearly expressed in the referendum, to withdraw from the EU without further primary legislation”.

Lord Pannick QCPH

Lord Pannick QC said Mrs May has no legal power to trigger Article 50 without prior authorisation

Attorney General Jeremy Wright, the Government’s leading law officer, is at the centre of the legal battle.

He has stated: “The country voted to leave the EU in a referendum approved by Act of Parliament.

“There must be no attempts to remain inside the EU, no attempts to rejoin it through the back door, and no second referendum.

“The result should be respected and the Government intends to do just that.”

Because of the urgency and constitutional importance of the case, any appeal is expected to be heard by the Supreme Court, the highest court in the land, before the end of the year.