Theresa May is facing a fresh Tory revolt that could force her into a humiliating U-turn on her plan to put the precise Brexit date into domestic law.

A last-minute amendment to the EU Withdrawal Bill is expected to win the support of pro-EU backbenchers who are furious that the move would deny them a proper “meaningful vote” on any final deal.

The potential rebels are the same Conservative MPs who forced the Government to agree to separate – amendable - legislation to implement any exit agreement, in Monday’s climbdown.

However, the latest revolt is far more serious for the Prime Minister, because she personally pledged, just four days ago, that the exit date, of 11pm on Friday 29 March 2019, would be on the face of the Bill.

Dominic Grieve, the former Tory Attorney General, has already branded the plan “thoroughly stupid”, because it would prevent a last-gasp extension to the exit negotiations, if they remain deadlocked.

The Tory rebels are angry that it makes a mockery of the promise of a vote on any deal, because that vote might come too late for Parliament to force a change of course – or prevent a no deal exit.

They met the Conservative chief whip last night, to ram home the message that further concessions will be needed in the days and weeks to come.

Britain will leave EU without deal if MPs vote down final deal, says David Davis

Nicky Morgan, the former Education Secretary, said Ms May’s plan showed she was “tone deaf and tin-eared”, while another former minister, Anna Soubry, vowed to rebel.

She revealed, about the meeting: “It was stormy because you have got people at that meeting who have never spoken out.

“The date going into the Bill has really upset a lot of really top-quality backbench Conservative MPs. These are people, a lot of them ex-ministers, highly respected, and they are genuinely cross about this.

Ms Soubry warned the Prime Minister: “There were some people there who have never rebelled and they are now talking, for the first time ever, of rebelling.”

The amendment has been tabled by Yvette Cooper, the former Labour Cabinet minister, who has opened talks with unhappy Conservatives. It could be debated as early as today.

It would not allow the Government to set Brexit day until Parliament has approved the new Withdrawal Agreement and Implementation Bill, enshrining the exit deal in law.

It would prevent MPs being denied a vote until after the UK has left and require ministers – if the deal is rejected - to go back to Brussels for better terms, by extending the Article 50 process if necessary.

The rebels are first likely to demand further concessions from David Davis, the Brexit Secretary. If unsuccessful, they could table their own amendment, or support Ms Cooper’s.

However, Robin Walker, Mr Davis’ deputy, stood firm early today, telling BBC Radio 4’s Today programme: “The UK will be exiting the EU at the end of March 2019, come what may.”

He refused to put a date on when MPs would get to vote on the outcome of the negotiations, saying only that it would come “as soon as possible after a withdrawal agreement”.

And, underlining that it remains a “take it or leave it” offer, Mr Walker vowed: “What we are talking about now is how we leave the European Union – not whether we leave the European Union.”