LONDON (AP) — Efforts to unseat British Prime Minister Keir Starmer from inside his own government broke out into open rebellion Thursday, with one potential rival resigning from the Cabinet and another clearing the way to enter any future leadership contest.

Health Secretary Wes Streeting became the first senior minister to quit Starmer 's Cabinet on Thursday in what is expected to be a precursor to challenging his leadership.

READ MORE: U.K. Prime Minister Starmer defiant as calls for his resignation grow

Starmer is facing growing pressure from his own Labour Party to step down after disastrous results for Labour last week in local and regional elections. The election drubbing cemented doubts among many Labour lawmakers about Starmer's judgment, vision and leadership ability –- a brutal indictment on a leader who returned the party to power in July 2024 after 14 years in opposition.

"You have shown courage and statesmanship on the world stage — not least in keeping Britain out of the war in Iran," Streeting wrote in an excoriating resignation letter. "But where we need vision, we have a vacuum. Where we need direction, we have drift."

"It is now clear that you will not lead the Labour Party into the next general election," he added.

Streeting, whose political ambitions have long been known, is considered one of a handful of people who could try to unseat Starmer. Doing so would not automatically spark a national election. Labour was elected for a five-year term, and British political rules allow parties to change leader without going to the country.

Another likely challenger, former Deputy Prime Minister Angela Rayner, said Thursday that she had reached an agreement with tax authorities to clear up questions about her taxes that forced her to leave the Cabinet last September. Rayner told the Guardian newspaper that Starmer should "reflect on" his position, adding that she was ready to "play my part" in any leadership election if Streeting were to trigger a contest.

Race to unseat Starmer heats up

Pressure for Starmer to step aside has intensified since Labour suffered heavy losses in local and regional elections last week, underscoring voter frustration with a government that has failed to deliver on pledges to boost economic growth and improve living standards for working people.

A stagnant economy and stubbornly high consumer price inflation have made it difficult for Starmer's government to deliver on its promises after winning a landslide election victory less than two years ago.

Starmer has vowed to remain in office, warning lawmakers that any leadership contest would plunge the government into "chaos" at a time it should be focused on issues like the cost of living crisis and war in the Middle East.

His effort to fight off a leadership challenge was bolstered Thursday morning by a rare bit of positive economic news.

Gross domestic product, a broad measure of economic activity, grew 0.6% in the first three months of the year, compared with 0.2% in the previous quarter, the Office for National Statistics said.

Treasury chief Rachel Reeves said the figures showed that her policies were working and that renewed economic growth would allow the government to put more money into public services and programs to support those hit by the high cost of living.

She said the party shouldn't put hard-won economic stability at risk "by plunging the country in chaos at a time when there is conflict in the world."

There was also positive news from the National Health Service. Figures showed that waiting lines for NHS appointments — one of Streeting's signature priorities — fell for the fifth straight month, something Streeting is likely to point to if he runs for leader.

Streeting comes from a faction of the left-leaning Labour Party that sees itself as the modernizing wing, as does Starmer. Rayner is a favorite of members who think the party has strayed too far from its working-class roots and those who want the party to do more to boost the minimum wage and raise taxes on the rich.

Under Labour Party rules, any potential challenger to the prime minister would have to have the backing of 81 of the party's 403 members in the House of Commons. More than that number have publicly called on Starmer to quit in recent days.

Other potential candidates may enter any race for the leadership.

Greater Manchester Mayor Andy Burnham is widely seen as a potential candidate, though he would have to find a way back into Parliament before he could run. Allies have suggested a sitting member of the House of Commons could resign to make way for Burnham to run in a special election.

Efforts to depose a Labour leader are relatively rare

While the opposition Conservative Party has a history of deposing prime ministers while in office, Labour does not, said Jonathan Tonge, a professor of politics at the University of Liverpool.

"They don't do ruthless on their leader,'' he said. "They don't tend to depose their leader. The Conservatives, they readily do ruthless.''

While there is a chance that the current efforts to unseat Starmer will fizzle out, that would probably just delay the crisis for a few months given the level of fragmentation in British politics, Tonge added.

If "a civil war opens up within a Labour Party that's supposed to be governing us at present, it's an extraordinary state of affairs given it's less than two years since Keir Starmer won one of Labor's greatest election victories ever," Tonge said.

"He's got a huge parliamentary majority, he's got more than 400 MPs, and yet his prime ministership may be on the brink of disintegration," he added.