Boris Johnson has survived an attempt by Conservative MPs to remove him from No 10, but more than 40 per cent of his party voted against him.
The prime minister won the no-confidence vote – triggered when 54 of his MPs demanded the contest – but the margin of 211 votes to 148 will only fuel doubts about his leadership.
It is significantly higher than the 120-130 rebels that were widely expected – and a far worse result than when Theresa May faced a similar contest.
One senior Tory warned of “a guerrilla war” in his party through to the next general election, with further attempts to topple Mr Johnson following the Partygate scandal.
And Rory Stewart, the former Conservative leadership candidate, predicted: “This is the end for Boris Johnson. The only question is how long the agony is prolonged.”
Mrs May won a no-confidence vote in December 2018 – but was forced to resign just five months later as the blow of 117 MPs turning against her sapped her authority.
Mr Johnson is braced for losing two crucial by-elections later this month and faces a Commons inquiry into whether he lied to parliament over the No 10 parties.
The result was revealed after all 359 Conservative MPs trooped into a Westminster committee room to take part in the secret ballot – their mobile phones confiscated to avoid photos emerging.
Cabinet ministers had rallied around, but some Scottish Tories deserted the prime minister – while Mrs May cast her vote, almost certainly against Mr Johnson, in a glittery blue ballgown.
Keir Starmer pointed to the result as fresh evidence of “divided Tories propping up Boris Johnson with no plan to tackle the issues you are facing”.
“I don’t claim that I or my party will get everything right, but I promise that when we don’t we will always be honest with you,” the Labour leader said.
Charles Walker, a former vice-chair of the 1922 Committee of Tory backbenchers, speaking before the result, said a large revolt would not see the party “get behind the prime minister”.
“Or will there be a temptation to sort of have a rolling maul, a guerrilla war, for the next six, 12, 18, 24 months?” he asked.
Ed Davey, the Liberal Democrat leader, called for Conservatives who care about “integrity and decency” to resign the party whip and sit as an independent.
“Whilst Boris Johnson has clung on today – make no mistake, his reputation is in tatters and his authority is now totally shot.”
But Nadhim Zahawi, the education secretary, claimed Mr Johnson had won a “handsome” victory, explaining: “It’s a ballot. 50 plus one is a majority. Boris did much better than that.”
The fact that all 359 Tory MPs took part means the MP arrested on suspicion of rape and other sexual offences and ordered to stay away from Westminster, voted through a proxy.