Plaid Cymru’s historic Caerphilly by-election win ends over a century of Labour dominance and signals a major shift ahead of next year’s Senedd election.
Plaid Cymru have pulled off a historic victory in the Caerphilly by-election, ending Labour’s century-long dominance in one of its safest Welsh strongholds.
The result marks the first time Plaid have ever held the seat in the Senedd, with veteran candidate Lindsay Whittle securing 15,960 votes to win comfortably ahead of Reform UK’s Llyr Powell (12,113 votes) and Labour’s Richard Tunnicliffe (3,713 votes), who slumped to a distant third.
The scale of Labour’s defeat, in a constituency they have held at every Senedd election since its creation in 1999, represents a major political shock in Wales and raises serious questions about the party’s grip ahead of next year’s Senedd election.
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Senedd Election Odds
Senedd Election - Most Seats Betting Odds
| Party | Odds |
|---|---|
| Reform | 5/6 |
| Plaid Cymru | 6/5 |
| Labour | 20/1 |
| Conservatives | 100/1 |
| Liberal Democrats | 250/1 |
| Green | 500/1 |
Correct as of 14:40 on 24/10/2025.
61% of bets through oddschecker are backing Reform to win Welsh Senedd Election since the conclusion of the Caerphilly by-election as their influence continues to grow.
Labour's odds have drifted from as short as 5/1 just two months ago to as long as 20/1 now.
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Who is favourite to win the Welsh Senedd 2026 Election?
Reform are 5/6 best price favourites with bet365 to win the Welsh Senedd 2026 Election.
The Caerphilly by-election highlights shifting dynamics across Welsh politics. Reform UK’s surge to second place, a dramatic leap from just 495 votes in 2021, underlines growing voter disillusionment with the established parties and suggests a volatile contest ahead.
Labour figures, including First Minister Eluned Morgan, admitted the result was “disappointing” and vowed to “learn the lessons” as the party faces renewed pressure to reconnect with voters on core issues such as the cost of living and public services.
