Theresa May accused in court of attempting to unlawfully start Brexit process by using ancient executive powers under Royal prerogative

THERESA May is accused of attempting to start the Brexit process by unlawfully using ancient executive powers under the Royal prerogative.

In one of the most important constitutional cases in generations, a QC at the High Court 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 and philanthropist living in London who voted Remain in the EU referendum on June 23.

Ms Miller is the lead claimant in a historic legal action with several other applicants, including the so-called "People's Challenge".

The campaign 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.

The Brexit legal challenge has been described as the most important constitutional case in generations.

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".

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."

This morning Conservative former minister Dominic Raab said the challenge was fuelled by a "special kind of arrogance".

He told BBC Radio 4's Today programme: "I think this is a pretty naked attempt to steal the referendum by the back door."

He added: "I don't think it's right that a fund manager with deep pockets and legal friends in high places gets to go to court and try and block or frustrate that process.

"I think it takes a pretty special kind of arrogance to think that one person's view trumps that of 33 million."

But Ms Miller said when she was given permission to launch her action: "This case is all about the sovereignty of Parliament.

“It is very important that the (Article 50) issues are dealt with in a serious and grown-up way.

"We are making sure that happens."