Plaid Cymru has flipped Caerphilly in a Senedd by-election held on 23 October 2025, securing 47% of the vote, with Reform UK second and Labour third. Turnout reached 50.43%, the highest for a Senedd by-election, a clear sign that the stakes for next May have cut through.

Lindsay Whittle took 15,961 votes (47.4%) to Reform UK’s Llŷr Powell on 12,113 (36.0%), while Labour’s Richard Tunnicliffe slid to 3,713 (11.0%). Plaid’s majority was 3,848 on a near-27-point swing from Labour, which held almost 46% here in 2021.

Reports from the count and post-vote analysis point to tactical voting by centre-left and some Conservative voters to block Reform, a pattern consistent with the minimal Green and Lib Dem tallies. Plaid’s leader Rhun ap Iorwerth also acknowledged an element of voters wanting to stop Reform.

Plaid framed the contest around practical fixes-fairer funding from Westminster, jobs and the NHS-while parking the timescale for independence. Ap Iorwerth has said repeatedly that this is not an independence election, with a route map to be set out separately.

For Labour, this is more than a bad night in one seat. Losing Caerphilly leaves Welsh Labour on 29 of 60 seats at Cardiff Bay and underlines wider vulnerability in its heartlands ahead of 2026. No 10 acknowledging public frustration with the pace of change only adds to the pressure.

Reform UK will point to rapid growth as proof it can convert national support into Welsh gains: from 495 votes here in 2021 to 12,113 and 36% last night. Yet finishing second after a high-profile push shows how an anti-Reform rally can harden late.

For households and SMEs, the winning message leaned into everyday economics. In 2025–26, retail, leisure and hospitality businesses continue to receive 40% business rates relief, and the non‑domestic rates multiplier rise is capped at 1%-modest but real help as costs pile up.

Structural change follows next year. From May 2026 the Senedd moves to 96 Members elected via closed‑list proportional representation across 16 six‑member constituencies. In that system, vote shares like Reform’s in Caerphilly would almost certainly deliver representation.

Locally, Caerphilly will sit within the new ‘Blaenau Gwent Caerffili Rhymni’ multi‑member area. Parties now have months to bank volunteers, funding and clear pledges on health, housing and the high street before the rules change.

The next test is close: the Senedd election is set for Thursday 7 May 2026. This result resets expectations and fundraising targets across Wales; for investors and local owners, near‑term signals to watch are business rates policy and the pace of public‑service delivery.