Economic decline and the cost-of-living squeeze in the UK are big political issues in the contest to replace Johnson.

The contenders needed the backing of 20 Tory MPs to secure a place in Wednesday’s first round of balloting. Senior Conservative lawmaker Graham Brady confirmed the names at a briefing in Westminster.

On a day of moves in Westminster, the high-profile candidate Grant Shapps withdrew and threw his support behind the early front-runner Sunak, who has the most publicly-declared support from Tory MPs. Former health secretary Sajid Javid, who resigned moments before Sunak last week, also pulled out, as did the relatively unknown Rehman Chishti.

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Home Secretary Priti Patel announced she would not stand, a move seen by many as a boost for Foreign Secretary Liz Truss’s bid to be the preferred candidate of the low-tax, Thatcherite wing of the Conservative Party.

Conservative MPs were due to cast their ballots, with the result of the first round to be announced about 5pm (12am Thursday Hong Kong time). The candidate with the least support is knocked out, along with anyone receiving fewer than 30 votes.

The second round of voting is scheduled for Thursday, with further rounds next week following television debates arranged for the weekend.

The Conservatives want the contest to be as rapid as possible, given the longer it goes on, the more the candidates’ attacks on each may impact the views of the wider electorate. The aim is to have a final two before July 21.

At that point, the process shifts to the estimated 175,000 grass roots party members who get the final say in who enters No 10 Downing Street in September. In that phase, it’s not Sunak but trade minister Penny Mordaunt who currently leads the way, according to a ConservativeHome survey.

Mordaunt was expected to formally launch her leadership bid on Wednesday.

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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

Sunak would also lose to Kemi Badenoch, who has the backing of Conservative big-hitter Michael Gove and is seen as a rising star of the Tory right, Truss and Attorney General Suella Braverman in a head-to-head vote among grass roots Tories, according to the ConservativeHome findings.

So far, the debate has focused on tax cuts, with many candidates trying to out-do each other in a bid to appeal to the Tory right, just as Johnson tried to do whenever his position came under pressure.

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Sunak’s major handicap is that he raised the UK’s tax burden to its highest level since the 1940s as chancellor to pay for pandemic-era spending, a record that sits uneasily with many Conservative MPs. In his final months in office before resigning, Sunak resisted calls to cut taxes for fear of fuelling inflation, which is forecast to exceed 11% in the UK in October.

But Sunak used his campaign launch to hit back at his Tory rivals, who he said were combining unrealistic tax pledges with spending promises.

“Once we have gripped inflation, I will get the tax burden down,” Sunak said in a speech in London on Tuesday. “It is a question of ‘when’, not ‘if’.”

And Sunak has rejected claims that as part of Johnson’s tarnished administration, he was not the fresh start he was claiming.

He said he had already responded to revelations about his wealthy wife – after it emerged that she was not paying UK tax on overseas income – and that he had a green card for US residency even while serving as chancellor.

Sunak and Johnson were both fined by police for attending a lockdown-breaking party in Downing Street.

Reuters, Bloomberg, Agence France-Presse