Why everyone in Welsh politics is talking about Caerphilly and what it means for 2026

A seismic shift may well be underway in Welsh politics. When the constituency of Caerphilly went to the polls on 23 October 2025, as part of the by-election triggered by the passing of Hefin David, it delivered a result that has sent ripples far beyond the valleys. 

The result

• 15,961 votes (47.4%) to Lindsay Whittle (Plaid Cymru) 
• 12,113 votes (36%) to Llŷr Powell (Reform UK)
• 3,713 votes (11%) to Richard Tunnicliffe (Welsh Labour)
• All other candidates received fewer than 1,000 votes each

Turnout stood at 50.43 %, the first time a Welsh Parliament by-election has recorded over half of eligible voters casting ballots.

Why this matters

For decades, Labour dominance in Wales has felt almost unshakeable. The structure of the existing electoral system, combined with traditional loyalties, meant that change was incremental, if at all. But as we noted in our earlier piece, the coming 2026 election is not just another contest. It introduces a new proportional system, with 16 super-constituencies returning six Members each, and the shift to a fully proportional voting system. 

The Caerphilly outcome suggests two things: first, that the “safe seats” may no longer be safe; second, that voters are willing to move away from traditional party loyalties. Plaid’s win in this by-election, in a seat Labour has held since devolution means that the terrain is changing. These results should be read as more than local. They are a signal of what may come in 2026.

What does it tell us about the direction for 2026?

• Momentum for smaller or non-traditional parties is building. Reform polling strongly here; Plaid making gains from Labour’s base.
• Labour’s dominance is under pressure. Holding government was becoming harder with 60 seats under the old system; in the new system, coalitions are likely.
• Voter engagement matters. A turnout above 50% in a by-election is rare, indicating that voters sense there is something important at stake.
• Campaign strategies will need to adapt. The by-election shows that local dynamics, voter fatigue, national issues and party identity all interplay in ways perhaps under-appreciated before.

Implications for communications, public affairs and reputation

For organisations and public affairs stakeholders in Wales, this election cycle will demand fresh thinking. Some key points to consider are:

• Don’t assume incumbent or dominant party advantage. The narrative of inevitability is gone.
• Messaging should account for voter fluidity and local context. The Caerphilly result underscores that voters will shift if their expectations are not met.
• Engagement must be broader. Record turnout in what would normally be a low-interest by-election signals that campaigns cannot simply rely on “usual voters”.
• Coalitions and alliances matter. With proportional systems, the communications narrative must include a broader ecosystem of parties, movements and alliances.
• Reputational risks increase. In a more contested environment, fewer safe seats means more surprises, and surprises draw media attention, which means higher reputational stakes for all actors.

Looking ahead to 2026

What happens in Caerphilly may well be repeated in towns and valleys across Wales next May.

If we see more seats flipped, or more votes switching, it will confirm that Wales is entering a new era of politics. For communicators, this means heightened uncertainty, but also opportunity. The rules of the game have changed, and the time to prepare is now.

It is no longer simply about holding ground, it is about winning hearts and minds. And as the Caerphilly result shows, those are up for grabs.