THERESA May is facing another parliamentary bust-up over her flagship Brexit legislation after a compromise designed to keep critics in her own party on board was denounced as “unacceptable” by Tory Remainers.

The move was branded “sneaky” by one backbencher while another senior pro-EU Tory said the wording of a government amendment was changed at the last minute to deny MPs the chance of blocking a no deal Brexit.

A senior minister was forced to deny having lied about the plan, which was signed off by May.

Peers are to vote on Monday on a proposal to give MPs the power to dictate the government’s response if it fails to reach a deal with Brussels.

May avoided almost certain defeat in the Commons on Tuesday by assuring rebels that their concerns about having a “meaningful vote” on the final Brexit deal would be addressed.

However, the amendment to the EU Withdrawal Bill tabled yesterday leaves Parliament facing a “deal or no deal” choice.

If MPs reject the agreement reached by May with Brussels – or if no deal has been obtained by January 21 – Parliament will be offered the opportunity only to vote on a “neutral motion” stating that it has considered a minister’s statement on the issue.

Crucially, the motion will be unamendable, meaning that MPs cannot insert a requirement for 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 indicated that the final text of the amendment tabled by ministers yesterday had been changed from the wording which he believed had been agreed earlier in the day. He said: “I think it is unacceptable because it seems to me to be contrary to what the whole intention was behind this whole amendment.”

Backbench Tory MP Sarah Wollaston tweeted: “So just to be clear we are now going to have to amend the ‘unamendable’ after the agreed amendable amendment acquired a sneaky sting in the tail.”

Solicitor General Robert Buckland acknowledged that previous versions of the amendment had existed until May decided on the final proposal yesterday afternoon.