After a mad dash back from his Caribbean holiday, a flurry of canvassing, secret summits with rivals Rishi Sunak and Penny Mordaunt, and a significant air war campaign, Boris Johnson announced shortly before 9pm last night that he would not run for PM after all.

It was the most Boris Johnson way of admitting defeat: I am a winner who could deliver a Conservative victory in 2024, I have the numbers (he claimed 102 supporters), I could do it if I wanted to, but now is not the time.

All weekend, his team had been saying that he had the numbers and was preparing to run – despite only having 59 public endorsements at the last tally.

‘Grateful’ Sunak reacts as Johnson backs down – live updates

So his withdrawal was a bit of a shock to some of his supporters. Conservative MP James Duddridge tweeted: “Well that was unexpected. Off to bed!”

There had been a lot of scepticism – and still is – as to whether Mr Johnson had really hit the required threshold of 100.

But what was far clearer was that the momentum is firmly with his rival Rishi Sunak, who now has more than 150 backers.

Support has come from all wings of the party – including, crucially, flagbearers on the right such as Lord Frost, Kemi Badenoch and Suella Braverman.

What became apparent over the weekend for Mr Johnson was that – while he had a core of support – the memories of July’s chaos, his resignation and the turmoil that followed is still very fresh in many MPs’ minds.

As one of his key backers put it to me last night: “The anti-Boris coalition is very vocal and he thinks two-thirds of the party are against him and it will make the party ungovernable, so he can’t do it, and it will go the way of Liz Truss.”

In his statement, Mr Johnson said as much – writing that he had “sadly come to the conclusion” that trying to get back into No 10 now wasn’t the right thing to do. “You can’t govern effectively unless you have a united party in parliament.”

While Mr Sunak was hoping to beat Mr Johnson by two to one among MPs, the former PM would have likely won the vote if Conservative Party members had their say.

The embattled Tories would then be in the worst of all worlds, with another PM the parliamentary party didn’t want.

There was a question mark over whether Mr Johnson would even be able to fill all the roles (up to 170 MPs) in his government given so many would simply not serve under him.

At least one MP said he would resign if Mr Johnson returned to No 10 in those circumstances – while there was talk of mass revolts, defections and even the possibility of a group of Tories collapsing the government in favour of a general election. Mr Johnson perhaps concluded he didn’t have a choice.

But seeds of disunity were visible in his statement last night. Mr Johnson’s remarks that he “reached out” to Rishi Sunak and Penny Mordaunt to “come together in the national interest” – but was spurned – is likely to agitate his most ardent backbench supporters.

This was Nadine Dorries last night: “Boris would have won members vote – already had a mandate from the people. Rishi and Penny, despite requests from Boris refused to unite which would have made governing utterly impossible. Penny actually asked him to step aside for her. It will now be impossible to avoid a general election.”

And just as Mr Johnson faced a tranche of diehard enemies on the backbenches, so will Mr Sunak – in the form of Johnsonites who will never forgive the man they believe brought about the downfall of the former PM.

Read more:
Why Johnson dropped out – in his own words
Could we get a new PM today? Key timings

It looks likely that Mr Sunak will be the next prime minister, having lost out to Liz Truss over the summer.

He could be declared as the new party leader at about 2pm should he be the only MP to receive 100 nominations.

There will, however, be a mad scramble for votes from Ms Mordaunt as she tries to use Mr Johnson’s withdrawal to get across the line and onto the ballot.

She currently only has 25 public backers so is a long way off – but some Johnson supporters might pivot to her, just to try and block Mr Sunak.

One figure familiar with the Johnson camp suggested last night that many of his backers might privately move over to Ms Mordaunt in the ballots to scupper Mr Sunak’s coronation.

And as for Mr Johnson, he might be reluctantly sitting this one out for now, but there is a hint in this statement – as there was when he quit with the words “hasta la vista baby!” – that he could be back: “I believe I have much to offer but I am afraid that this is simply not the right time.”

Will he stay in parliament and sit it out for when, if ever, it is?