Labour is set to lose a seat in a Welsh heartland for the first time in over a century as voters flock to Reform UK and Plaid Cymru.
Tonight's is only the fifth ever by-election for the Senedd since devolution - but few have sparked such fear inside Sir Keir Starmer's party.
Multiple Labour sources have already admitted they are expecting to lose the Caerphilly by-election tonight - with a turnout confirmed at 50.3 per cent.
A Reform UK insider, meanwhile, told GB News: "It's going to be tight - but hopefully we do it."
Party leader Nigel Farage and his Plaid Cymru counterpart Rhun ap Iorwerth were both in the town this week for a last-ditch campaign.
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The result in Caerphilly could be a bellwether for the Senedd election next May - and will certainly be treated as such by the winning party.
The by-election was called following the sudden death of Hefin David, who had served as Caerphilly's MS since 2016.
PICTURED: Reform UK's Llyr Powell with party leader Nigel Farage in the Welsh town
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PICTURED: Plaid Cymru leader Rhun ap Iorwerth with candidate Lindsay Whittle
|PA
A Welsh Labour spokesman said: "Hefin David loved this constituency and its people. He’s been at the heart of our campaign throughout.
"This has been a tough campaign for the party for a variety of reasons, but we’re proud of what our staff and volunteers have achieved over the past six weeks and are committed to continuing to fight for Caerphilly and the Valleys."
The result is expected to come in between 2am and 3am, however if the result is close as some pollsters have predicted, there could be a recount.
Sources within both Reform and Plaid have predicted a tight call between the two parties.
READ MORE ON REFORM UK:
Count verifiers look on as counting begins for the Caerphilly Senedd by-election
|PA
While Labour is the largest party in the Senedd, it does not have a majority, and the next budget vote in January could be even more difficult if the party loses the Caerphilly seat.
Speaking at a press conference in Caerphilly last month, Nigel Farage announced Reform’s candidate, Llyr Powell, and pledged to "throw everything" at the campaign in Caerphilly.
Plaid Cymru’s candidate, Lindsay Whittle, is a long-standing councillor in the Penyrheol ward and leader of the group on Caerphilly Council.
The Labour candidate is Richard Tunnicliffe, a financial analyst and publisher. The candidates fielded by other parties are Gareth Potter, for the Conservatives, Gareth Hughes, for the Green Party, and Anthony Cook for Gwlad, a Welsh pro-independence party.
Steve Aicheler is running for the Liberal Democrats and Roger Quilliam is the candidate for Ukip.
One Labour source described the expected defeat in Caerphilly as a "defeat for Starmerism, not for First Minister Eluned Morgan."
They said that Baroness Morgan, who has served as First Minister since August 2024, had been relatively popular on the doorsteps.
However, they warned that the FM needed to "assert herself" and differentiate Welsh Labour as much as possible from the party in Westminster the run-up to next May's.
Labour Senedd members are expected to hold a crunch meeting on Friday morning.
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