Plaid Cymru has won the Caerphilly Senedd by-election, ousting Labour with a decisive victory and relegating Reform UK to second place. The result marks a historic shift in Welsh politics, as Plaid’s Lindsay Whittle secured 15,961 votes, while Reform’s Llŷr Powell garnered 12,113. Labour’s Richard Tunnicliffe saw the party’s vote collapse to just 3,713 in what was previously a safe seat.
Plaid leader Rhun ap Iorwerth hailed the win as a choice of “hope over division and progress over the tired status quo”, declaring his party the only force capable of stopping “billionaire-backed Reform”. The party described the result as a “seismic political shift”, signalling a new two-horse race between Plaid and Reform ahead of the 2026 Senedd election.
Labour figures acknowledged the blow, with deputy first minister Huw Irranca-Davies insisting the party would bounce back and focus on bread-and-butter issues. He called on Plaid to engage in budget talks, noting the by-election loss makes it harder for Labour to pass its 2026-27 budget. Reform’s Powell said the campaign had honed the party’s grassroots operations, vowing to apply lessons in the next election.
Polling expert Sir John Curtice said Plaid is now well-placed to lead the next Welsh government, but cautioned against writing off Reform. The by-election was triggered by the death of Labour’s Hefin David, with Whittle pledging to follow in his predecessor’s footsteps.
