[PRIMER] UK Gorton & Denton by-election. Polls close at 22:00GMT, exit polls due thereafter. Results expected around 04:00GMT on 27th February.

The by-election serves as a formal litmus test on the fortunes of the UK Labour Party and, by extension, PM Starmer. As a reminder, Starmer has been under significant pressure and scrutiny in recent weeks as more details emerge around, and the fallout continues, re. Mandelston/Epstein and Starmer. Ahead of the by-election, Starmer himself has described it as a straight contest between Reform and Labour.
However, the by-election is regarded as a very close one to call due to specific factors and as such the Greens, Reform, or Labour could conceivably win. While Labour not-winning might not be a fatal blow for Starmer, a poor result could spark a return to recent pressure on the PM and would likely see the odds of a Labour leadership-election being “scheduled” by March 31st increase from 1%; for reference, the current odds of one by June 30th (i.e. in the aftermath of the May local elections) stands at just 10%. Note, the emerging view with the Labour party appears to be that it is perhaps, on balance, worth leaving Starmer in his position regardless of how the by-election goes, and then reassessing the situation at that point.
As it stands, the likely favourite within Labour to succeed Starmer would be former deputy Rayner. However, her stance as a ‘soft leftʼ member of the party means she is a less market-friendly option, as the assumption is that she would increase public spending via greater taxation, vs the current Starmer/Reeves administrationʼs approach. Polymarket odds on there being another PM in 2026 imply a 38% probability of no-change, followed by Rayner on 19% and Wes Streeting on 11%; note, the probability of Rayner replacing Starmer in 2026 has been as high as 20% in recent weeks.