Sir Roger Gale told Sky News' Kay Burley that he left because of the tone of the behind-closed-doors meeting - in contrast with the contrition expressed by Mr Johnson in parliament earlier.

The meeting began with the ritual banging of desks and saw Mr Johnson launch into an immediate appeal for party unity and support as he battles critics following his fine last week for breaching lockdown rules.

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Sir Roger, a long term critic of the PM, said: "I stayed for three minutes and left. I didn't storm out in a huff.

"I found the tone of the meeting from the very beginning very different from the tone in the House of Commons.

"I'd gone expecting a serious meeting about serious issues.

"I didn't expect a lot of bluster and pantomime performance and I'm afraid that's what I heard and it seemed to me that my time was better spent doing other things.

"I did not like the tone of the meeting.

"I'm told that the meeting got more serious later and certainly some colleagues asked fairly searching questions.

"But what I heard, I didn't care for too much."

Asked whether he thought the PM did not take the issue seriously enough, Sir Roger said: "I think you could say that, yes."

The MP, who has previously said that Mr Johnson's position is untenable, has also expressed the view that now is not the right time to replace him given the war raging in Ukraine.

But he added: "My hope and expectation would be that if things get markedly worse for the prime minister then he will do the honourable thing and resign."

Tuesday night's meeting also saw the PM hit back at the Archbishop of Canterbury, Justin Welby, for criticising his plan to send asylum seekers to Rwanda.

He said the churchman had "misconstrued" the plan and should be condemning Vladimir Putin instead, a senior government source told Sky News.

That was on Wednesday described as a "disgraceful slur", if true, by the Church of England's head of news, John Bingham.

Meanwhile, Mr Johnson is preparing to face Prime Minister's Questions - likely to mean a second day of pressure in Parliament over the partygate affair.

On Thursday, MPs will again focus on the issue as Labour tables a motion to refer the matter of whether the PM broke the ministerial code for an investigation by a parliamentary committee - though Mr Johnson himself is scheduled to be away in India.

That investigation would focus on whether the prime minister knowingly misled the Commons when he initially claimed that no lockdown rules had been broken over partygate, but will require the support of Tory MPs to go ahead.

The prime minister received a fixed penalty for attending a gathering on his birthday in June 2020 and Downing Street is braced for him to face further fines linked to other events under investigation by police.

Business minister Paul Scully, speaking on Sky News, defended Mr Johnson's conduct during lockdown-breaking events.

Mr Scully said: "The prime minister interpreted what he felt was the law, the guidance at the time.

"He took his decision in the heat of the moment but he's accepted he's done wrong, he's accepted he's made a mistake - and he's made a full apology - 30 times yesterday in his statement."

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Labour's deputy leader Angela Rayner reiterated her anger towards the prime minister and urged Tory MPs to act.

She told Sky News: "Nobody is above the law in this country and this prime minister needs to recognise that, his MPs need to reinforce that - because if they don't they undermine our democracy."