A majority of MPs will back Theresa May and trigger Article 50 regardless of today’s High Court ruling, a campaign group predicted.

The People's Pledge, the cross-party campaign that pushed for the EU referendum, said a sufficient number of MPs had switched to Leave to give the Prime Minister a majority in the Commons.

Ahead of the June vote, a survey of all 650 MPs found that 480 of the UK’s 650 MPs were voting Remain, including a majority of Conservatives.

That suggests Ms May could have run into trouble in the Commons if the Supreme Court backs the High Court and rules she has no power to bypass Parliament before invoking Article 50.

However, the People's Pledge said its research had found that 258 MPs had already said they would vote for Article 50, if the Commons is given that opportunity.

A further 94 Conservative MPs had yet to indicate their view, but the vast majority of Tories were widely expected to abide strictly by the referendum result.

With a majority requiring 322 votes – excluding the Speaker and his three deputies – it left Ms May only needed the backing of 64 of those 94 MPs to win in the Commons, the research said.

Stuart Coster, co-founder of the People's Pledge, said: “The sudden conversion of these Remain campaigners to championing parliament's powers is a startling turnaround in their views.

“A majority of MPs also supported Britain remaining in the EU, but the public's clear backing for Brexit has, rightly, changed outlooks amongst those who, above all, respect democracy.”

However, the prediction leaves open the possibility that some MPs who originally backed Remain will be emboldened to stick with that view, following the High Court ruling.

Today, one Labour MP, Stephen Kinnock, said he would not vote for triggering Article 50 if the terms put forward by the Government were "not in the national interest".

Another, frontbencher Barry Gardiner, said he would give no guarantee “until we see the whites of ministers’ eyes”.

Owen Smith, the defeated leadership candidate, called on Labour to amend any Article 50 Bill to “give the British people the final say on real terms of Brexit”, in a second referendum.

But Hilary Benn, the Labour MP who chairs the Commons Brexit Committee, asked if he would back Article 50 if there was a vote now, replied: “Yes.”

Mr Benn said the Commons was only seeking the chance to influence the negotiating stance, adding: “This was not a judgment on whether we are leaving the European Union – because we are.

“The public made that choice in the referendum and I think Parliament should uphold that.”

Ed Miliband said MPs should vote on Ms May’s strategy, tweeting: “Today’s ruling shows Govt cannot bypass parliament. It must be used to ensure a parliamentary vote on negotiating plan to leave the EU.”