Disastrous results for the governing Labour Party in local elections last week have plunged Britain into a new crisis, just under two years after Starmer won a large majority on a vow to bring stability and end a decade of political chaos.
After days of calls by Labour lawmakers for Starmer to quit or set out a timetable for his departure, Wes Streeting resigned as health minister on Thursday, the first senior minister to break cover. He said he was standing down because "it is now clear you will not lead the Labour Party into the next general election".
While Streeting did not trigger a formal contest, potential rivals to the prime minister, such as Greater Manchester mayor Andy Burnham, started positioning themselves for a possible leadership challenge that Starmer has said he will fight.
Streeting criticised his former boss in a resignation letter which said he was standing down to allow a wide debate about what comes next, one which the Labour movement wanted to focus on ideas rather than personalities or factions.
"It needs to be broad, and it needs the best possible field of candidates," Streeting wrote.
"Where we need vision, we have a vacuum. Where we need direction, we have drift," Streeting said in pointed remarks about Starmer.
"Leaders take responsibility, but too often that has meant other people falling on their swords."
A source close to Streeting said the former health minister had enough support to mount a formal leadership challenge but had not triggered an immediate contest because he felt it would be preferable for Starmer to set out an orderly timetable.
Starmer responded with a letter expressing regret Streeting had stepped down, saying "it is incumbent on all of us to rise to what I see as a battle for the soul of our nation" and "turn the page on the chaos".
He swiftly appointed one of his supporters, James Murray, as Streeting's replacement.
The British leader has said he will battle to keep his job, and sources close to him say he is determined to fight any leadership contest. The pound edged lower after Streeting's resignation and news that Burnham would seek to return to parliament.
Another possible candidate in any leadership contest, Starmer's former deputy, Angela Rayner, said earlier on Thursday she had been cleared of deliberate wrongdoing over her tax affairs, an impediment to challenging the prime minister.
Another potential candidate is armed forces minister Al Carns, a former Royal Marine seen by some in Labour as a new face who could freshen up the party.
But Starmer still enjoys some support. Education Minister Bridget Phillipson repeated her backing for Starmer and suggested the rest of his cabinet team of top ministers were also supportive.
"This is now a chance for us to pause, take a breath as a party and try and draw a line under all of this," she said.
Starmer has adopted a "business-as-usual" approach and finance minister Rachel Reeves warned lawmakers against plunging Britain into chaos when its anaemic economy was turning a corner. The economy grew unexpectedly in March.
Business leaders fear another leadership race to choose what would be Britain's seventh prime minister in about a decade would deter investment - something the Labour government has said must improve to turn around Britain's fortunes.
