Former Chancellor of the Exchequer Rishi Sunak and Foreign Secretary Liz Truss will battle it out to become Britain's next prime minister after they won the final lawmaker vote, setting up the last stage of the contest to replace Boris Johnson.

International Trade Minister Penny Mordaunt was knocked out in the final round of balloting among Conservative lawmakers. Sunak won 137 votes,  and Truss received 113.

The contest to succeed Johnson will now go before the Conservative Party's 200,000-odd dues-paying members, who will select the winner later this summer in a mail-in ballot. The winner, to be announced on September 5, will automatically become prime minister.

Though Sunak has won each of the five rounds of voting by lawmakers, a YouGov poll published on Tuesday showed that he was less popular with the party's grassroots. He is predicted to lose to Truss, a favorite of the party's right wing, in the head-to-head contest.

Sunak said on Twitter: "Grateful that my colleagues have put their trust in me today. I will work night and day to deliver our message around the country."

He helped steer the economy through the pandemic, but some party members have blamed him for triggering Johnson's downfall with his resignation earlier this month.

He has also faced criticism on everything from his record in government to his wife's wealth.

Truss thanked some lawmakers outside parliament shortly after the votes were announced. "I am in it to win it," she said to reporters. In a statement, she added, "As prime minister I would hit the ground running from day one, unite the party and govern in line with Conservative values."

On Sunday, she admitted she might not be "the slickest presenter" but "when I say I'll do something, I do it."

She has insisted that she was bound by the cabinet's "collective responsibility" when asked about Johnson's controversies. She will be hoping there are enough Tory members who believe the prime minister has been ill-treated by the party after he won an emphatic 80-strong majority in parliament at the last general election in 2019, the biggest win for the Conservatives since 1987.

Both candidates have made pledges on tax cuts as the cost-of-living crisis continues to bite. However, Sunak dismissed as "fairytales" his rivals' promises of immediate tax cuts, arguing that inflation must be brought under control first. Inflation in the UK rose by 9.4 percent in June, hitting a fresh 40-year high, official statistics showed on Wednesday.

The Tory leadership race was triggered after Johnson was forced to step down on July 7 by an avalanche of resignations of government officials, who protested against his scandal-plagued leadership. Johnson continues to serve as caretaker prime minister until a new Tory leader succeeds him. 

(Cover: Former UK Chancellor of the Exchequer Rishi Sunak (L) and Foreign Secretary Liz Truss. /CGTN)