THERESA May is facing her biggest parliamentary bust-up yet on the Brexit Bill after a promised compromise designed to keep critics in her own party on board was denounced as "unacceptable" by Tory Remainers.

One pro-EU Conservative branded the Prime Minister’s strategy "sneaky" while another claimed the wording of a new UK Government amendment was changed to deny MPs the chance of blocking a "no-deal" Brexit and sending UK ministers back to the negotiating table should Westminster reject the final agreement.

Earlier this week, Mrs May avoided an almost certain Commons defeat by inviting potential rebels into her private office and assuring them that their concerns about having a "meaningful vote" on the final Brexit deal would be addressed.

Yet the PM’s new amendment to the EU Withdrawal Bill, tabled Thursday evening, leaves Parliament facing a stark "deal or no deal" choice.

It says if MPs rejected the final agreement, then Parliament would be offered the opportunity only to vote on a "neutral motion," saying MPs had considered a minister's statement on the matter.

Crucially, this motion would be unamendable, so MPs could not order Mrs May to go back to the negotiating table, extend the Brexit transition or revoke the UK's withdrawal under Article 50.

Leading pro-EU Conservative Dominic Grieve said he believed, after a very sensible negotiation with the PM, there had been an agreement, but “at the last moment part of the text was changed to make the final motion unamendable…It is unacceptable.”

Mr Grieve tabled his own amendment, enabling MPs to dictate the next steps the Government should take in the event of a no deal.

It has now been re-tabled in the Lords, setting the scene for a fresh Government defeat when the Bill returns there on Monday; another Commons showdown will occur when it goes back before MPs on Wednesday.

Labour’s Keir Starmer said: "Theresa May has gone back on her word and offered an amendment that takes the meaning out of the meaningful vote. Parliament cannot - and should not - accept it."

Tom Brake for the Liberal Democrats said the PM had been “caught red-handed” making conflicting offers. “We are now finding out which lie she was telling.”

But the Brexit Department stressed the new Government amendment met the tests set down by the PM ie any changes to the Bill must not undermine negotiations or change the constitutional roles of Parliament and Government and they must respect the referendum result.