A second turn in Number 10 for Boris Johnson would be “a guaranteed disaster”, one of his former supporters has claimed.

Northern Ireland minister Steve Baker revealed to Sky News’ Sophy Ridge that he would be backing Rishi Sunak in the upcoming Tory leadership contest as he would “deliver competent, capable, professional government that we can rely on”.

But the influential MP also launched a scathing attack on the ex-prime minister, saying a return to Downing Street for Mr Johnson was “bound to implode, taking down the whole government with him”.

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His remarks come as the race to get onto the ballot nears its climax following the resignation of Liz Truss after just 44 days in office.

Candidates to replace her only have until 2pm on Monday to secure the backing of 100 MPs as the expedited race seeks to calm turmoil in the party.

So far, Mr Sunak is leading the pack, already breaking the threshold needed to make it to the next stage.

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But while only 57 have publicly stated their support for Mr Johnson, one of his backers, Northern Ireland Secretary Chris Heaton-Harris, insisted to Ridge that he “definitely” had the numbers to make it onto the ballot.

The ex-PM also won the support of another cabinet minister this morning, with Nadhim Zahawi insisting he had “got the big calls right” and “learned from [previous] mistakes how he could run Number 10 and the country better”.

However, the only person to have officially declared their candidacy so far is Commons leader Penny Mordaunt, who has received 23 public endorsements.

Damian Green, who served as Theresa May’s de-facto deputy, told Ridge she was “attracting support from all wings of the party” and would create “calm stability” for the Conservatives.

And he said he was confident she would reach the threshold by Monday, saying she was “in it to win it”.

Mr Sunak and Mr Johnson are understood to have held talks last night amid speculation they could strike a deal over the leadership.

But Mr Green also warned against the race being “stitched up behind closed doors by big figures at Westminster”, telling Ridge: “Penny doesn’t need to do deals to unify the party and stabilise the government because of what she stands for and because of the work she has done.

“She can do that herself and that, I think, makes her the strongest candidate.”

Mr Heaton-Harris sang the praises of the ex-PM to Ridge, adding: “This is a time when we need a big player like Boris in our politics so I think he will.”

He said Mr Johnson is “keen to see what the parliamentary party thinks”, adding: “He is a great unifier, he is a great campaigner, he is someone who has a solid sense of what the country wants to hear and what the country needs to happen.”

However, Mr Baker – once leader of the influential European Research Group of Brexiteer Tory MPs – warned the impending investigation into whether the former PM misled the Commons over Partygate could throw the party into chaos again.

He told Ridge: “I’m afraid the trouble is because of the vote [over whether to accept the findings], Boris would be a guaranteed disaster.

“In that vote it’s guaranteed there’ll be a large number of Conservatives who will refuse, as they see it, to lay down their integrity to save him, and at that moment his premiership will collapse.”

He added: “It’s a guaranteed nailed-on failure and we cannot allow it to happen.”

Instead, he said Mr Sunak would be the best person for the job, adding: “Above all, what we need is stability. We need professionalism. We need to move this country forward from a position of great difficulty. And Rishi’s the right guy to do it.”

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