Boris Johnson urged to drop comeback bid as he lags ever further behind rival Sunak

Boris Johnson is coming under pressure from within his own party to ditch his attempted comeback as prime minister, amid fears that he could pit activists against MPs in a way that would tarnish the Conservative brand for a generation.

Withdrawal from the race to succeed Liz Truss as Tory leader would almost certainly lead to the coronation on Monday of Mr Johnson’s main rival Rishi Sunak, who formally announced his candidacy on Sunday with a promise of “integrity, professionalism and accountability”.

The former PM was tonight lagging far behind Mr Sunak in the battle for MPs’ endorsements, and had shown himself unable to unite the right behind his banner, as totemic figures like Steve Baker and Suella Braverman threw their lot in with the former chancellor. He is yet to declare himself a contender.

Penny Mordaunt rejected Mr Johnson’s appeal to drop her own leadership bid and offer him her backing, telling him that the bulk of her supporters would in any case switch to backing Mr Sunak.

And polling guru Prof Sir John Curtice told The Independent that Mr Johnson’s election-winning ability – the main plank of his supporters’ case for a second premiership – is no longer the gold dust it was in 2019.

Sunak supporters were sceptical of the Johnson camp’s claim that he had the 100 MPs’ nominations required to get onto the ballot paper, after just 60 made their names public.

Mr Baker warned that a second Johnson premiership would be a “guaranteed disaster” and would collapse before the year was out due to the upcoming contempt inquiry into the former PM’s alleged lies over Partygate.

He urged Mr Johnson to wait until after the conclusion of the privileges committee investigation before attempting a return to the political front line.

And senior backbencher Andrew Murrison told The Independent that the time had come for Mr Johnson to throw in the towel.

“For the sake of party unity, Boris needs to understand that the game is up and now is not his time,” said Dr Murrison, who served in Mr Johnson’s administration but quit as a minister in July in protest at the then prime minister’s conduct.

“Pulling out now would be the most dignified and statesmanlike thing to do.”

With Mr Sunak’s endorsements fast approaching the 179 figure, which would give him the majority of the parliamentary party, Dr Murrison said he believes party members will fall in behind the clear choice of MPs in the online ballot to choose between the final two candidates left standing on Monday.

But others in the Sunak camp fear that, if Mr Johnson can survive the MPs’ round of the contest, members will once again favour the most right-wing candidate over the one most popular in parliament, as they did in the summer.

There have been warnings that this could split the party, with MPs saying they would refuse to serve in a Johnson government, or even refuse to take the whip, and that they would instead sit as independents or defect to other parties.

While securing the endorsement of cabinet ministers like James Cleverly and Nadhim Zahawi – the latter just 108 days after he told Mr Johnson to quit in July – the former PM was by Sunday evening trailing Mr Sunak by around 90 nominations.

But close ally Jacob Rees-Mogg insisted: “I have been speaking to Boris Johnson, and clearly he’s going to stand, there’s a great deal of support for him.”

In an 8am phone call with MPs, Mr Johnson insisted he did not regard the privileges committee inquiry, which will require him to give evidence in front of TV cameras in the coming weeks about lockdown-breaching parties at Downing Street, as an obstacle to his return.

He insisted he would cooperate with the inquiry, and said that the process, which could lead to his suspension from parliament and a recall by-election, should be allowed to run its course.

But Mr Baker said the investigation would lead to the implosion of a Conservative government for the third time in a matter of months.

He added that Tory MPs, mindful of the need to preserve their reputations given that they might face a hunt for a new job after the election, would refuse to “lay down their integrity to save [Mr Johnson]” if they were required to vote on punishments recommended by the committee.

“At that moment his premiership will collapse,” said Mr Baker. “It’s a guaranteed, nailed-on failure, and we cannot allow it to happen.” He said Mr Johnson should do “something big and statesmanlike” and put his political ambitions on hold until the process is complete.

The endorsement of Mr Sunak by Mr Baker, an arch-Eurosceptic, may deliver another nail in the coffin of Mr Johnson’s comeback hopes, if the European Research Group of Tory MPs follow his lead when they meet early on Monday to decide who to back.

The decision of Ms Braverman to back Mr Sunak was another heavy blow to Mr Johnson’s hopes of victory. A champion of the right and an ERG stalwart, who had been thought to be mulling her own bid for the leadership after resigning as Ms Truss’s home secretary, Ms Braverman said: “I have backed Boris from the start.

“But we are in dire straits now. We need unity, stability and efficiency. Rishi is the only candidate that fits the bill and I am proud to support him.”

And Prof Curtice cast doubt on expectations that returning Mr Johnson to No 10 would pay electoral dividends for the Conservatives. “Johnson’s popularity – never as high as is often suggested – is not what it once was,” said the polling guru, of Strathclyde University. “On becoming prime minister, his net satisfaction rating was -7. By the time he left office at the beginning of July, it stood at -45.”

Since his precipitous fall from public affection, Mr Johnson had “never shown any sign of being able to repair the damage” caused by Partygate, said Prof Curtice.

And he questioned Mr Johnson’s supporters’ claims that he continues to hold a mandate from the 2019 election, won on the back of a promise to Get Brexit Done.

“By the end of his time in office, support for the party among Leave voters was down to just 51 per cent,” said the professor. “In truth, the ‘mandate’ Johnson won in 2019 has not aged well.”