A “war cabinet” could be formed insteading of holding a leadership contest if Boris Johnson is deposed as Prime Minister, a senior Tory has suggested.

Roger Gale said the “interim administration” could be led by the deputy prime minister, Dominic Raab, who briefly took the reins in 2020 when Johnson was hospitalised with Covid-19.

The veteran Conservative MP previously submitted a letter of no confidence in the Prime Minister, which remains “on the table”, but has since said it is not the right time for a leadership election, given the situation in Ukraine.

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He is now keen to establish if it may be possible to put a contest on hold if Johnson resigns or is forced out of his job.

It comes as the PM enters another week determined to defend his premiership as he prepares attempt to deflect criticism over partygate by pointing to the war in Ukraine.

While he acknowledged the UK is not currently at war, Gale told the PA news agency “we’re pretty damn close to it”.

He said an alternative name for the arrangement could be a “crisis cabinet”.

“I don’t actually know whether what I’m proposing is possible legally,” he said.

“But if Johnson were to resign – he probably won’t – but if he were to resign, then … if the deputy prime minister led a ‘war cabinet’ to deal with the crisis and get us through to the point when we could then have a proper leadership election, that is a possible way forward.

“What I don’t know is what the situation is if the Prime Minister refused – suppose it was necessary for the Prime Minister to go but he won’t resign, then insofar as I’m aware the only way of doing that is by getting the 50 letters … and then hope that you can win a no-confidence motion, which is not certain.”

He added: “What I don’t know under the rules is if you have a no-confidence motion and the Prime Minister goes, do you then have to have a leadership contest?

“Or could you have what I’m suggesting, which would be an interim administration – a Conservative administration, but an interim administration – to see us through?”

Despite being fined by the Metropolitan Police for his birthday bash held in the Cabinet room in June 2020, while coronavirus restrictions were in place, the Prime Minister is expected to tell MPs on Tuesday that this should not be the focus of politicians.

Gale said if “another three or four fines” were to follow, and the anticipated Sue Gray report into the saga is “damning”, then the point could be reached where “all credibility is now gone – he has got to go”.

Gale said he has not changed his mind on the PM’s position since submitting his letter to the backbench 1922 Committee, but claimed the war had changed his priorities. 

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“When I was last speaking there wasn’t a war in Ukraine,” he said.

“Now there is. And that war is potentially nuclear – it really is that serious.”

He added: “If there’s a leadership contest, there’s no coronation this time: there’s no one person who is going to obviously take over as leader of the Conservative Party.

“You can put the deputy prime minister in as interim prime minister, as happened when Johnson was ill. That’s perfectly achievable because you don’t have to have an election to do that.

“But if you have a leadership contest, then what are we talking about? Liz Truss, Foreign Secretary; Ben Wallace, Defence Secretary; Michael Gove, supposed to be in charge of Ukrainian refugees and levelling up; very possibly Sajid Javid, Health Secretary; and others from the Cabinet … possibly still even Rishi Sunak.

“Are we seriously saying that in the middle of this crisis we’re going to take all those eyes off the ball?”

He said: “If the Prime Minister’s credibility is shot to hell and there has to be something done, then my suggestion for a way forward would be an interim administration led by the deputy prime minister, and what effectively I have called, in shorthand, a ‘war cabinet’.

“Now, at the moment we are not technically, of course, at war, but we’re pretty damn close to it. And I think that might be a viable way forward.

“But I haven’t put this to anybody – I haven’t tried to fly it within the 1922 Committee or anything.”

Johnson is said to be preparing to make a statement in the Commons once MPs return to Westminster following the Easter recess.

Opposition parties are expected to try force a vote on the Prime Minister in an attempt to hold him in contempt of parliament. 

The Times reported that the PM was set to focus on Ukraine, the cost-of-living crisis and a trip to India which will focus on defence and trade.

As well as addressing MPs in the Chamber, the newspaper said Mr Johnson would speak to a meeting of the entire Conservative parliamentary party on Tuesday evening.

Lindsay Hoyle, the Commons Speaker, is also expected to decide if to allow a vote on whether to refer Johnson to the Privileges Committee – which would decide whether he had misled the House over his partygate explanations.