Gina Miller warns Theresa May of new court battle if Parliament not guaranteed vote on leaving EU

The woman who forced Theresa May to consult MPs on triggering Article 50 has warned ministers they could face a new Brexit court battle if they do not allow Parliament a final vote on quitting the EU.

Gina Miller raised the prospect of further “legal challenges” if the Prime Minister refuses to rewrite her Article 50 bill to guarantee Parliament a final vote.

Ms Miller told The Independent that the Supreme Court judgement in the case her team won against the Government, demands MPs approve any move to leave the bloc following negotiations – whether on terms Ms May agrees or with no deal secured at all.

The Lords is considering similar legal advice from constitutional experts which states Ms May will need further legislation after negotiations finish on any move to pull Britain out of the EU.

The Government suffered its first defeat in Parliament on the Brexit bill after the Lords a plan to guarantee the rights of EU citizens living in the UK, against Ms May’s will.

Ms Miller argued ministers were setting themselves for another court fight if they do not allow a guarantee for the vote to be written into the Article 50 bill now.

She said: “As the Supreme Court ruled in my Article 50 case, only Parliament has the constitutional authority to authorise, and give legal effect to, the changes in domestic law and existing rights that will follow from the negotiations.

“This means a promise or resolution simply will not do. As Lord Hope stated on the 21 February in the House of Lords debate ‘As the Supreme Court said in Miller, at paragraph 123, a resolution of Parliament is an important political act, but it is not legislation’.”

Paragraph 123 of the judgement states that “only legislation which is embodied in a statute will do” when it came to the case.

Ms Miller added: “Would it not be easier for the Government to accept the amendment for a vote at the end of the negotiations in 18 months’ time now, rather than facing legal challenges in 18 months’ time?

“The Government tried to ignore the law once before, doing it twice would be incredibly careless.”

Three of the UK’s most senior EU law experts, Sir David Edward, former judge of the European Court of Justice, Sir Francis Jacobs, the court’s former Advocate General, and Sir Jeremy Lever, recently published legal opinion supporting a similar idea dubbed the “Three Knights Opinion”.

Their advice read: “The constitutional requirements for a decision by the United Kingdom to leave the European Union include the enactment of primary legislation consenting to give legal effect to the terms of a withdrawal agreement between the United Kingdom and the European Union, or authorising the United Kingdom’s withdrawal from the European Union in the absence of any such agreement.

“Only Parliament has the constitutional authority to authorise, and give legal effect to, the changes in domestic law and existing legal rights that will follow from that decision.”

Ms May has said she will put the terms of her final deal to a vote in Parliament but has made clear that if they are rejected the UK will leave the EU with no deal – something that runs contrary to the legal advice and has been criticised as a false choice.

Senior Labour backbencher and supporter of the Open Britain campaign, Chuka Umunna, said ministers had to accept the amendment to the Article 50 bill that would allow Parliament a vote on Ms May’s deal.

He added: “It is completely unacceptable for the Government to only offer Parliament a ‘bad deal or no deal’ ultimatum at the end of the negotiations. It’s the parliamentary equivalent of being asked whether you would prefer to lose an arm or a leg.”

“The Government should accept the amendments that give Parliament a meaningful vote and a real choice at the end of this process.”

Any changes approved by the Lords, where the Government is in a minority, would still have to be approved by the Commons, where Ms May does command a slim majority.

Home Secretary Amber Rudd has already said she does not think there is any possibility of ministers amending the Article 50 bill.

A Government source told The Independent: “Article 50 tips us out of the EU after the two year period, if no extension has been unanimously agreed by the other 27, without a deal, and certainly not with another bill in Parliament.”