One Tory MP said: “The DUP want her head on a plate.”
It comes as Mrs May’s deputy, David Lidington, insisted the confidence and supply agreement with the DUP remains in place despite the party’s ten MPs failing to back the government in crucial recent votes.
The Prime Minister’s one-time allies in the DUP have said they will vote down her Brexit deal on Tuesday, and will only support her in a vote to collapse the government if the deal fails.
“They see her as duplicitous,” one Conservative MP said, adding that they believed events next week could lead to a snap general election.
Another Tory MP suggested the confidence and supply agreement with the DUP had been fatally damaged by the Northern Irish party’s support for a motion of contempt over Brexit legal advice.
“I don’t see how it can survive the DUP supporting the contempt motion,” the MP said.
Mr Lidington visited north Belfast yesterday to sell the Prime Minister’s Brexit deal and said he had received assurances of support from a senior member of the Democratic Unionists within the last 24 hours.
DUP leader Arlene Foster has said a Commons amendment supported by backbench Tories giving Parliament a say on invoking the Irish border backstop does not go far enough, adding that domestic “tinkering” to the Withdrawal Agreement would not persuade her party’s ten MPs to back the government.
Mr Lidington said: “The DUP have made it clear that they see the confidence and supply agreement as continuing.
“As with any minority government there are going to be squalls and difficulties in a Parliament where the government does not have an automatic majority in either House, but that is not something new to British history.”
The parliamentary arithmetic is against the government ahead of next week’s withdrawal treaty vote.
Following an amendment, Parliament would decide whether to trigger the backstop arrangement or extend the transition period beyond December 2020.
Mr Lidington said MPs have a public duty to act in the national interest. “The choices are not going to go away as a consequence of postponing the vote,” he said.
“The European Commission, the president of France, the chancellor of Germany, other leaders, have all said, very plainly, this is the deal that is available. So they are not going to move, so the choice becomes if not this deal, what else?”
With the Commons vote on Mrs May’s Withdrawal Agreement expected to result in it being rejected by MPs, the risk of a no-deal Brexit could increase.
Former foreign secretary Boris Johnson said the Brexit deal obtained from Brussels by Mrs May is similar to the conditions that might be imposed on the defeated side in a war.
As the Prime Minister sent senior colleagues out around the country to sell her deal, Mr Johnson repeated his call for MPs to throw it out in the Commons vote.
The Prime Minister was coming under growing pressure to delay the 11 December vote to give herself time to ask for more concessions from the EU at a Brussels summit at the end of next week.
With three days of the five-day debate complete, analysis showed that of 163 MPs who have spoken, just 27 have indicated they will back Mrs May’s deal compared with 122 – including 29 Tories – who will vote against.