Main public face of Brexit makes shock announcement hours after his key ally Michael Gove launched his own campaign

Boris Johnson has unexpectedly ruled himself out as a candidate for Britain’s next prime minister, after the justice secretary, Michael Gove, sent shockwaves through Westminster with a last-minute bid for the Conservative leadership.

Gove had been chairing Johnson’s leadership campaign, after the two men worked shoulder to shoulder in the campaign for Britain to leave the EU.

But with just hours to go before formal nominations closed at noon on Thursday, Gove announced that he no longer believed Johnson was the right man for the job, and that he would launch his own bid to be the next prime minister.

Despite having been the leading public face in the victorious Vote Leave campaign, Johnson quickly concluded he could not command enough support from his party, after a series of key lieutenants, including the business minister Nick Boles and the pro-Brexit MP Dominic Raab, defected to the Gove camp.

He stuck to plans to hold a mid-morning press conference at a London hotel, and delivered a defiant speech saying Britain should take last week’s Brexit vote as an opportunity to “think globally”, and “lift our eyes to the horizon”. But he concluded by saying he would no longer put his name forward.

“Having consulted colleagues and in view of the circumstances in parliament, I have concluded that person cannot be me,” he said, stunning MPs who had assembled to show their support.

Johnson’s backers, who had gathered in the hotel to lend their support to the former mayor, appeared shocked by his announcement, after he spent much of his speech setting out a pitch to be a one-nation Tory.

“This is not a time to quail, it is not a crisis, nor should we see it as an excuse for wobbling or self-doubt,” Johnson said of Britain’s vote to leave the EU, before he announced he was not planning to stand.

Gove is now widely regarded as the main rival to Theresa May, the home secretary, who had launched her own campaign earlier on Thursday with a pledge that “Brexit means Brexit”, and that there would be no general election until 2020.

The other contenders are the work and pensions secretary, Stephen Crabb, the former defence secretary Liam Fox, and the pro-Brexit energy minister Andrea Leadsom.

The first round of voting will take place on 5 July, with the weakest candidate eliminated in successive rounds, until the field is whittled down to two candidates, who will be presented to the Conservatives’ grassroots members. The result will be announced on 9 September.

A source close to Johnson said: “He’s proud to have been one of those who led the campaign for Brexit, and he’s absolutely proud that it’s given voice to millions of Britons who have previously felt ignored.

“His role now will be to champion that cause; to ensure that those commitments made by our leaders to the people and the message sent by the people to our leaders is heard.” They added that he would fight to ensure that politics does not return to “business as usual”.

Conservative leadership race: who are the five candidates? Read more

Gove’s allies said he had had growing doubts about Johnson’s ability to build a future government in recent days, and over how he would manage the complex negotiations that will be required to extricate Britain from the EU. They suggested he lacked the “focus and grip”, to succeed in No 10.

Johnson’s backers in parliament suggested the late timing of Gove’s intervention was a long-planned act of treachery. “Anyone can see who has wielded the knife, and how it has been wielded,” a source said.

Gove’s statement said: “I have repeatedly said that I do not want to be prime minister. That has always been my view. But events since last Thursday have weighed heavily with me.”

He added: “I wanted to help build a team behind Boris Johnson so that a politician who argued for leaving the European Union could lead us to a better future.”

Ed Vaizey, one of the MPs who attended a meeting with Gove on Thursday morning, said: “He was ready to back Boris; but the closer it got, the harder he thought about it, he thought, it’s not the right person. Follow that through to its conclusion: the logic is, if he doesn’t think Boris can do it, he has to step up to the plate and do it.”

Vaizey added: “I think he will be a better prime minister than Theresa May.”