Wes Streeting, until recently the Health Secretary and one of Prime Minister Keir Starmer's closest allies, has publicly asked Starmer to step back and think about whether he should remain in charge. According to the BBC, this is the clearest sign yet of trouble within the Labour party at the top.

Starmer's response was swift. He told supporters he would fight any attempt to remove him, and said that a leadership battle would hurt Britain. He is not going quietly.

Streeting has not formally announced he wants to replace Starmer. But because Streeting was recently sitting in the cabinet, his public challenge carries real weight. It is very different from a junior MP complaining on the sidelines. When senior figures break ranks, it changes the conversation.

A by-election in Makerfield, a constituency in Greater Manchester, is now at the centre of all this. Starmer plans to campaign there personally to help Andy Burnham, the Mayor of Greater Manchester, win the seat. If Burnham wins, Starmer has said Labour should then focus on finding a new mayor for Manchester.

But here is where it gets interesting: Burnham himself said he would run for Labour leader if a contest happened. This means the by-election is not just about a local vacancy — it could help decide who leads the party next.

Starmer's plan to campaign alongside Burnham in Makerfield — announced in late May — appears designed to tie them together. By linking himself to Burnham's success locally, Starmer makes it harder for Burnham to later claim he is a fresh alternative to Starmer's leadership. His comments about what comes next for Manchester, published on 17 June, follow the same logic: he is framing this as local politics, not as a springboard for Westminster ambitions.

Burnham is a popular figure in Greater Manchester and appeals to voters Labour has lost elsewhere. If he runs for leader, this would not be a token challenge easily dismissed.

Whether an actual leadership contest happens will depend on two things: the rules Labour uses to trigger a contest (which require a certain number of MPs to sign up), and whether the by-election result gives wavering MPs a reason to act. Streeting's public words make it much harder for them to ignore the question.

The real problem for Starmer is this: he is now defending his job while running a by-election campaign and dealing with questions about Manchester's future. That is a lot to juggle. The argument that a leadership fight would damage the country is something any Prime Minister under pressure would say — but it only works if his own MPs believe it. Once senior people start speaking out, the numbers become harder to predict.

What happens in Makerfield will not settle everything. But it will determine what the Labour party talks about next.