Reform UK and the Green Party are eyeing victory in 2026's first parliamentary by-election, as Sir Keir Starmer faces internal revolt over the decision to block Greater Manchester mayor Andy Burnham from standing for Labour.
The Gorton and Denton by-election is to take place on 26 February.
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It was called after suspended Labour MP Andrew Gwynne decided to stand down, and many saw it as a chance for ambitious and popular Mr Burnham to return to Westminster.
But Labour's ruling National Executive Committee has decided not to allow him to run for the seat, which is located in Greater Manchester, therefore ending - for now at least - any chance of a leadership bid.
The prime minister defended the decision, saying it would have diverted party resources away from May's local elections, and potentially force another by-election for Mr Burnham's mayoralty.
Sky's chief political correspondent Jon Craig said in a meeting of the Parliamentary Labour Party on Monday night, the attorney general - a key ally of Sir Keir - had to bat off "plenty of gripes" from MPs about the decision.
Craig said many believe the prime minister "has bungled this badly", treating Mr Burnham "unfairly" and also "made himself weaker".
Attorney General Lord Hermer told colleagues he did not underestimate the challenge the party faced, but insisted the government's policies will "take hold" and "chance this country for the better and for the long-term".
What happened last time?
Labour won the Gorton and Denton seat with a majority of 13,413 in the 2024 general election - over half the vote.
Reform came second on 14.1%, and the Greens were third with 13.2%.
Both believe they can win when voters go to the polls next month.
Labour face 'anti-Starmer vote'
Nigel Farage said his party will announce its candidate today, and that "an anti-Keir Starmer vote" will prove crucial.
"There would have been a pro-Burnham anti-Starmer vote, that won't be there any more, and I think the anti-Starmer vote will come to us," he said.
Read more from Sky News:
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Sky's political correspondent Alexandra Rogers understands the Greens will announce a candidate on Sunday, but leader Zack Polanski won't be standing.
While he has a claim to northern roots (he was born in Salford), Polanski lives in Hackney, north London, and it's understood he's more likely to run for a seat in the capital.
But he is expected to visit the constituency this week.
A party source said: "We're throwing the kitchen sink at this, and believe we can win."
(c) Sky News 2026: Reform and Greens eye major by-election scalp amid Burnham row
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