Boris Johnson on Thursday lost the support of one of his most influential backbenchers, who declared that he cannot forgive him over the “partygate” scandal.

Steve Baker acknowledged that he had “systematically” helped Mr Johnson to become Conservative leader and secure an 80-seat majority at the 2019 general election.

On Tuesday, Mr Baker said the Prime Minister “could not have made a more humble apology” to the Commons after his police fine, while seeking assurance that “nothing of this kind will ever happen again”.

But 48 hours later, the MP for Wycombe accused Mr Johnson of a lack of “permanent contrition” for urging critics to focus on “things that make a difference to the electorate” rather than Downing Street parties.

Mr Baker said: “The reason that he is not long gone is because removing a sitting prime minister is an extremely grave matter, and goodness knows people will know I’ve had something to do with that, too.

“It’s an extremely grave matter and an extremely big decision, and it tends to untether history. And that’s why I’ve been tempted to forgive. But I have to say now, the possibility of that, really, for me, has gone.

“I have to say I’m sorry that for not obeying the letter and spirit – and I think we have heard that the Prime Minister did know what the letter was – the Prime Minister now should be long gone. I’ll certainly vote for [Labour’s] motion. But really, the Prime Minister should just know the gig’s up.”