Britain's Prime Minister Keir Starmer announces his resignation to the media outside 10 Downing Street in London on Monday. (AP Photo/Kin Cheung)

LONDON (AP) — British Prime Minister Keir Starmer said Monday he will resign, forced out by his own party after missteps and mistakes soured voters’ goodwill following a landslide election victory two years ago on a promise of steady leadership and economic growth.

Starmer says he will remain caretaker prime minister until his Labour Party chooses a new leader — with expectations growing that it will be former Greater Manchester Mayor Andy Burnham.

Burnham confirmed on social media that “I will put myself forward as part of this process.” Former Health Secretary Wes Streeting, who was considered his main rival for the top job, said he will back Burnham.

It was Burnham’s victory in a special parliamentary election last week that triggered Starmer’s decision to resign, as Labour lawmakers flocked to the charismatic former mayor in the hope he can revive the party’s fortunes. After nearly a decade as mayor of the northwestern city, Burnham returned Monday to Parliament, where he took the oath of office in the House of Commons. Only members of Parliament are eligible for the party leadership.

Streeting’s statement makes it more likely that Burnham will be selected without a leadership contest.

Burnham was cheered loudly by lawmakers — and heckled by one, who shouted “He’s not the Messiah!” — as he was sworn in, before posing for selfies and a group photo with dozens of Labour MPs in another part of Parliament.

Britain’s next election does not have to be held until 2029. Asked if he would call an early vote if he becomes prime minister, Burnham said: “You’re jumping several hurdles ahead there.”

Starmer is the sixth prime minister in a decade to stand outside No. 10 Downing St., and announce a departure. His statement came the day before Britain marks the 10th anniversary of its vote to leave the European Union, a decision that still roils the country’s economy and politics.

After weeks of insisting he would fight to keep his job, Starmer conceded to growing pressure to hand over to a new leader who can try and revive the government’s flagging fortunes. He led Labour to a landslide election victory in July 2024, but since then his popularity and that of the party have plummeted.