Former British Finance Minister Rishi Sunak whose resignation helped trigger a revolt that saw Prime Minister Boris Johnson agree to step down after a series of scandals, described himself as the underdog in the contest to become Britain's next prime minister on Saturday.

Members of the ruling Conservative Party will vote for a successor over the summer, with an announcement due on Sept. 5.

Sunak led all rounds of the voting among party lawmakers to reduce the field to two candidates.

However, it is Foreign Secretary Liz Truss who seems to have gained the advantage so far among the 200,000 members of the governing party who will ultimately choose the winner.

Truss held a 24-point lead over Sunak in a YouGov poll of Conservative Party members published on Thursday.

"Be in no doubt, I am the underdog," Sunak said in a speech in the central England town of Grantham, the birthplace of former Prime Minister Margaret Thatcher. "The forces that be want this to be a coronation for the other candidate, but I think members want a choice and they are prepared to listen."

Truss would be only Britain's third female prime minister after Thatcher and Theresa May, while Sunak would be the country's first leader of Indian origin.

So far the campaigning focus has been on pledges, or non-pledges, to cut taxes at a time when many people are struggling, as well as defence spending and energy policy.

In his speech, Sunak laid out what he called "common sense Thatcherism," promising careful management of the economy before tax cuts.

He questioned the morality of immediate tax cuts proposed by Truss at a time of soaring inflation and criticised as arbitrary her pledge to increase defence spending to 3% of gross domestic product (GDP) by 2030.

Truss says tax cuts are needed to stimulate growth.

"It is wrong to take money from people that we don't need to take when people across the country are struggling with the cost of living crisis," she told reporters in Kent, south east England, after meeting party members.

In an interview for Saturday's Times newspaper, Sunak said he would put the government on a crisis footing on taking office.

Truss has also promised to scrap all remaining European Union laws that still apply in Britain by 2023.