Theresa May’s fate could be decided as early as tomorrow, after a showdown meeting with her backbenchers was brought forward.

Graham Brady, the chairman of the backbench 1922 Committee, said he did not want MPs to have to wait until Tuesday for the crucial inquest with the Prime Minister.

As support drains away from Ms May, amid reports of a Cabinet plot to replace her, it sets the scene for her having to convince MPs face-to-face that she deserves to survive in No 10.

Backbenchers are also likely to demand to know why Downing Street announced that a deal was done for the Democratic Unionists to prop up the Conservatives in government – only to be forced to retract the claim overnight.

And they will want their fears of being tarred by association with the anti-gay marriage, anti-abortion Northern Ireland party eased.

“One of the things I've said to the Prime Minister is it's very important that she speaks to colleagues as soon as possible,” Mr Brady told the BBC.

“We were going to have a meeting of the 1922 committee on Tuesday, I'm hoping to bring that forward to tomorrow now so that she can talk to colleagues about that deal.”

Mr Brady also admitted that key sections of the Tory manifesto – including new grammar schools – could be ditched after the party saw its Commons majority disappear.

The comments came as former Chancellor George Osborne described the Prime Minister as a “dead woman walking”, predicting she could have fallen by the middle of the week.

Mr Osborne was joined in predicting Ms May's demise by former Education Secretary Nicky Morgan, who said a leadership contest could be held within weeks.

“I suspect that it could be over this summer and I think it should involve our party conference as well,” she told ITV's Peston on Sunday programme.

“I think we do need to have a debate in the Conservative party, we need a period of reflection after what’s happened in the last few days. We need to understand exactly where we’re headed.”

Another former minister, Anna Soubry, told Sky News: “I just can't see how she can continue in any long-term way. I think she will have to go, unfortunately.”

However, Ms Soubry predicted Ms May would not leave No 10 “for some time”, adding: “Let's get this clear, we need stability.”

It would require 15 per cent of Conservative MPs – a total of 48 – to write to Mr Brady to trigger a vote of no-confidence in her leadership.

But Michael Fallon, the Defence Secretary, dismissed suggestions that Ms May was fighting for her political life, insisting Tory MPs would “rally behind her and give her their support”.

Asked if she was a “dead woman walking”, he said: “I don’t agree with that. She won the biggest share of the vote since the 1987 election, for over 30 years.”

The Prime Minister is reported to have been in “floods of tears” as her election disaster unfolded, but Sir Michael said: “I don’t know about that”