The rules and timetable for the contest to replace Johnson are due to be set out next week by a party committee.

Sunak said in his resignation letter it had become clear that his approach to the economy had been too different to Johnson’s, as the two had tried to agree on the next steps for the country.

He continued on that theme in his candidacy announcement video.

“The decisions we make today will decide whether the next generation of British people will also have the chance of a better future,” he said.

“Do we confront this moment with honesty, seriousness and determination? Or do we tell ourselves comforting fairy tales that might make us feel better in the moment, but will leave our children worse off tomorrow?”

Johnson quit as leader of the ruling Conservative Party on Thursday, after a frenzy of nearly 60 resignations in less than 48 hours in opposition to his scandal-hit reign.

But the 58-year-old, whose three-year premiership has been defined by Britain’s departure from the European Union and Covid, said he would stay on until his successor is found.

A timetable for the leadership contest is expected on Monday, with the winner installed in time for the party’s annual conference in early October.

Defence Minister Ben Wallace was among the early front runners, a YouGov poll of Tories suggested. Conservative MP Tom Tugendhat and Attorney General Suella Braverman have both officially announced their candidatures, while Brexiteer Steve Baker has signalled interest.

Former health and foreign secretary Jeremy Hunt, who lost to Johnson in 2019, was “virtually certain” to run again, a source close to Hunt told British media.

03:45

Boris Johnson’s rise to power and what led to his downfall as UK prime minister

Boris Johnson’s rise to power and what led to his downfall as UK prime minister

In a defiant resignation speech in Downing Street on Thursday, Johnson said he was “sad … to be giving up the best job in the world”.

But he said he initially refused to surrender to his “herd” of Tory critics by claiming a personal mandate he won by a landslide in December 2019.

Even while eyeing the exit, Johnson sought to steady the ship, making several appointments to replace departed cabinet members.

At a first meeting of his hastily convened new top team, Johnson confirmed his lame-duck status by saying “major fiscal decisions should be left for the next prime minister”, Downing Street said.

Sunak and health secretary Sajid Javid prompted the exodus by quitting late Tuesday, just as Johnson apologised for appointing a senior colleague facing sexual assault claims to a prominent role.

Chris Pincher resigned as deputy chief whip last week following accusations he had drunkenly groped two men.

Downing Street officials eventually conceded that Johnson had known about other allegations against Pincher back in 2019, and many ministers recoiled at having to defend the PM yet again.

Is ‘hubris syndrome’ the reason why Boris Johnson took so long to resign?

As late as Wednesday night, Johnson – whose landslide 2019 win was the biggest Tory victory since the heyday of Margaret Thatcher in the 1980s – had been defiantly clinging to power.

But he was forced to concede his time was up after another round of resignations on Thursday morning and warnings of a second no-confidence vote next week by Tory MPs.

The Tory infighting erupted as millions of Britons battle the worst slump in living standards since the 1950s, fuelled by rocketing energy prices on the back of the war in Ukraine.

Johnson’s popularity had slumped since revelations about lockdown-breaking parties in Downing Street that saw him become the first prime minister to be fined in office.

Labour leader Keir Starmer and Rayner were themselves under investigation by police in northeast England over a gathering during lockdown, and had both vowed to resign if fined.

Durham police said Friday they were issuing no fines against Starmer, Rayner or 15 others at the April 2021 meeting, ruling it was a work event, not a party.