Steve Baker, the Conservative MP who plotted to oust Theresa May as prime minister, said it could be “checkmate” for Boris Johnson as he clings on to power.

The seasoned rebel ringleader and Brexiteer said the allegations of rule-breaking parties in Downing Street during coronavirus restrictions are “appalling”.

He said the Prime Minister “must go” if it is found he broke the law or lied to Parliament, but said “we are all waiting” for senior civil servant Sue Gray to publish her inquiry’s findings.

Some Conservative MPs have already publicly called for Mr Johnson’s resignation and one has defected to Labour, but others are for now holding fire.

Mr Johnson has apologised for “misjudgments” but insisted he thought a “bring your own booze” gathering in the No 10 garden during the first lockdown would be a “work event”.

Mr Baker told the BBC’s Political Thinking with Nick Robinson podcast: “It’s a sorry situation we’re in. I’m appalled we’ve reached this position.

“We didn’t make Boris Johnson Prime Minister for his meticulous grasp of tedious rules but this is appalling and the public are rightly furious.

“At the moment I’m afraid it does look like checkmate but whether he can save himself, we’ll see.”

Asked what he means by checkmate, Mr Baker added: “I feel a bit like we are all looking at the chessboard and you know how it goes – check, check, check, checkmate, and then people are all looking at the board, unless they are grandmasters, and saying, well is it over? And I think that is sort of where we are.

“It probably is checkmate and we are all waiting for Sue Gray’s report at the moment.”

So far, Tory opponents of Mr Johnson are short of the 54 letters required to be sent to the chairman of the 1922 Committee of Conservatives to trigger a vote of no confidence.

Mr Baker was instrumental in forcing such a vote against Mrs May over her Brexit Withdrawal Agreement in December 2018.

She survived the vote by 200 Tory MPs to 117, but ultimately was forced to stand down within six months.

Mr Baker said he would not “organise against” the Prime Minister, saying he is not duty-bound to be “leader of every insurrection”.

Instead he said he is “looking to the Cabinet for leadership”, adding: “We’re talking about alleged serious breaches of the ministerial code, possibly the law, possibly the Nolan principles of public life.

“Really there are some proper grown-ups, who are supposed to be leaders of our country, in the Cabinet, I would quite like them to rise to this moment.”