Betting markets are pricing in a 32% probability that Keir Starmer will no longer be prime minister by Thursday, rising to 57% by the end of May and 87% by the end of the year, as a Cabinet-level rebellion threatens to overwhelm his attempts to cling on.
Polymarket, the prediction platform, has seen $20 million in trading volume on the question, with the December contract surging from around 25% in mid-April to near-certainty in a matter of weeks.
The crisis deepened overnight after Home Secretary Shabana Mahmood privately urged Starmer to consider a departure timetable, following a similar intervention from Energy Secretary Ed Miliband, suggesting the Cabinet support that had protected his position is now crumbling.
More than 70 Labour MPs have publicly called for Starmer to resign or set out a timetable for his departure, not far short of the 81 signatures needed to trigger a formal leadership contest under party rules.
Four junior government members resigned on Monday evening, including aides to Health Secretary Wes Streeting and Deputy Prime Minister David Lammy, while backbencher Catherine West declared she was collecting names to force a leadership election in September.
Starmer attempted to steady the ship in a speech on Monday, taking responsibility for Labour's loss of more than 1,400 council seats in last week's local elections, most of which went to Reform UK.
He argued that constantly changing leaders would inflict chaos on the country and vowed to prove his doubters wrong.
But the speech was widely dismissed as insufficient, with West calling it "too little, too late" and calling for an orderly transition.
The leading contenders to replace him include Streeting, former deputy prime minister Angela Rayner and Greater Manchester Mayor Andy Burnham, though Burnham would first need to win a parliamentary seat.
Streeting is thought to have already secured significant support among Labour MPs, though no candidate has formally declared.
Starmer won a landslide in July 2024, ending 14 years of Conservative rule, but his popularity has collapsed amid the cost-of-living crisis, welfare cuts and the fallout from the Epstein scandal involving former US Ambassador Peter Mandelson.