Wes Streeting is preparing to resign from the cabinet and mount a formal challenge for the Labour leadership, with sources close to the health secretary indicating the move could come as early as Thursday. If he proceeds, it would represent the most serious internal threat to Keir Starmer's premiership since Labour took office.

The challenge has been in preparation for some time. Under Labour party rules, a challenger must secure nominations from 81 MPs before a leadership contest can be formally triggered. Downing Street briefed on Wednesday that Streeting had not reached that figure, though his allies rejected that assessment, arguing that firm commitments are rarely made until a candidate has publicly declared. A source close to Streeting confirmed that calls were being made to prospective supporters on Tuesday evening.

Streeting met Starmer briefly at Downing Street on Wednesday morning. His office declined to comment on the substance of the meeting, stating that he did not wish to distract from the King's Speech. No public statement followed from either side.

Those close to the Prime Minister said Starmer had long anticipated a challenge from Streeting and had consistently doubted he could command sufficient support within the parliamentary party. One cabinet ally was direct about the mood inside government, describing the situation in notably combative terms while noting that Starmer himself remained composed. The remark reflected the degree of frustration running through parts of the cabinet loyal to the Prime Minister.

Pressure on Starmer had been building before Wednesday. Zubir Ahmed, a minister and close Streeting ally, resigned from his post on Tuesday. He returned publicly the following day to argue that Starmer's authority had deteriorated beyond recovery. Ahmed's resignation was read by many in Westminster as a signal that Streeting's camp was shifting from private discontent to open action.

The King's Speech offered a brief interruption to proceedings. Constitutional convention makes it difficult for internal government disputes to dominate coverage during a state opening of parliament, and Streeting's office cited this explicitly as the reason for remaining quiet. Westminster sources expect events to move quickly once that moment has passed.

The central question is whether Streeting can convert what his allies describe as broad sympathy among Labour MPs into the formal written nominations that a contest requires. There is a familiar pattern in Westminster of MPs encouraging a potential candidate privately while declining to commit on paper. One MP close to Streeting's camp acknowledged the uncertainty, saying they were not certain the numbers were genuinely in place. Warm words and a signed nomination form are not the same thing, and that gap has ended leadership bids before they formally began.

Starmer has made clear he intends to fight. He issued a public ultimatum earlier this week, demanding that those with ambitions either act or stop destabilising the government. That Streeting appears to have read it as a prompt to move, rather than a reason to stand down, suggests the attempt to draw a line has not produced the intended effect.

Whether Thursday brings a resignation letter or another day of managed uncertainty, the government enters the remainder of the week in a state of open internal conflict. Neither side appears positioned to resolve it quickly, and the longer it continues, the more it occupies the political space the government would prefer to fill with policy.