Sir Keir Starmer is privately weighing whether to stand down as Prime Minister if Andy Burnham wins the Makerfield by-election and mounts a leadership challenge, senior Labour sources have said. Loyalists who have spoken to Sir Keir in recent days say he is far less defiant behind closed doors than in public, keeping “all options” open as he prioritises stability.

A Cabinet minister loyal to the Prime Minister told The Telegraph: “I don’t think he’s been defiant at any point. That is not his personality. He is trying to feel his way through what is the most responsible way forward here for the country... He is very much an all-options-on-the-table type of person.”

Sir Keir has publicly warned against the “chaos” of an open leadership race. Allies are urging him not to resign before the by-election — expected as early as June 18 — to prevent a damaging free-for-all. Downing Street insists he will fight on and would automatically appear on the ballot in any contest.

The path to Westminster for Mr Burnham cleared further on Friday when Labour’s National Executive Committee granted him permission to stand in the Makerfield selection. Josh Simons is stepping down as MP to make way for the Greater Manchester Mayor. Applications close on Monday and the NEC is expected to endorse a candidate on Thursday.

If elected, Mr Burnham is widely expected to challenge Sir Keir for the leadership. While Makerfield is traditionally safe Labour territory, the party faces a fierce battle. Mr Simons held a majority of just 5,399 over Reform UK in 2024. This month’s local elections saw Reform sweep every ward in the constituency with around 50% of the vote to Labour’s little more than a quarter.

Mr Burnham's name recognition could prove decisive. He enjoys a net favourability rating of +24% across the North West, according to Ipsos — far higher than Sir Keir, other party leaders or Labour itself. A Survation forecast suggested Labour is more likely to hold the seat with Mr Burnham as candidate, but would likely lose it without him. Reform UK and the Greens have already begun candidate selection.

Both Angela Rayner and Ed Miliband are expected to back Mr Burnham and forgo their own ambitions if a contest is triggered. Deputy leader Lucy Powell told The Guardian: “Mr Burnham’s 'story' and 'connection to the place' would be central to holding the seat.”

Education Secretary Bridget Phillipson described Mr Burnham as a “strong candidate” with whom she has worked closely on skills and SEND reform, while pledging to campaign for whoever Labour selects and offering Sir Keir her “full support”.

Wes Streeting, who quit as Health Secretary this week, backed the return of Mr Burnham, saying: “Labour needs 'our best players on the pitch'.”

Allies say he will run in any leadership contest to ensure “the broadest set of candidates possible”. He is due to make his first public appearance since resigning at a conference on Saturday. The hard-left Socialist Campaign Group may also field a candidate.

A former adviser to Sir Keir said: “Mr Burnham is interested in 'one job and one job only'.” One centrist minister suggested Sir Keir could target a September departure ahead of party conference.

The Times reported that Sir Keir is considering approving an £18 billion boost to defence spending next week as he battles to save his premiership.

A Government spokesperson said: “The delayed plan would be published 'as soon as possible' to deliver 'the best kit' to forces while growing the economy.”

Jess Phillips, who stepped down as safeguarding minister on Tuesday, said: “The situation feels 'very untenable'. Keir’s got to start making clear his vision for the country. He tried this week, and it didn’t work.”

Markets are already jittery. On Friday, 30-year gilt yields hit a 28-year high of 5.8 % amid fears of further instability.