Plaid Cymru’s byelection victory in the Welsh town of Caerphilly is unprecedented. Labour had won every election here for more than a century. Yet the result also feels strangely familiar.
Observers of British politics have become accustomed to waking up to unprecedented results. By the end of the previous Westminster parliament, record byelection swings against the incumbent government had become the norm, and elections at all levels had shown an electorate who were willing and able to identify the best-placed party to defeat a disliked option.
Byelections for constituency seats in the Senedd are rare. Since its establishment in 1999 (as the National Assembly for Wales), there have been only five, including the one held on Thursday.
In all previous cases, a member from the incumbent party was elected. With Labour dominance in the Welsh government, and in terms of Welsh seats in Westminster, it has been rare for there to be much interest in Welsh politics outside Wales.
However, the scent of a historic Labour defeat in its Welsh heartlands meant this time it was different. Whether prompted by the intense campaigning, the promise of change in an area dominated by a single party for a century, or voters motivated to ensure their least-liked party did not win – the turnout was significantly higher than the previous Senedd election in the seat, or indeed the national turnout at Senedd elections.
At 47.4% of the votes cast, this was not just a win for Plaid Cymru, but a convincing one. It was expected to be much closer. The only constituency poll of the campaign had Reform UK in the lead, while national polling for next year’s Senedd elections has Plaid and Reform neck and neck.
The result will be a disappointment for Reform UK. They will emphasise that their vote share, at 36%, is above their current polling for the Senedd and keeps them on course for a significant number of seats after May’s proportional representation-based (PR) elections. But having chosen to launch their 2024 general election manifesto only 20 miles away, in Merthyr Tydfil, this is not the result they were hoping for.
The result points to a new kind of electorate, who are far more willing to vote for “smaller” parties, in 2024 as the two-party share (the proportion won by Labour and the Conservatives combined) dropped below 60% for the first time. In Caerphilly, this was certainly a two-party race – but neither of the supposed main parties were in it (a combined vote share for Labour and the Conservatives of just 13%).
We can never be sure how voters switched between parties without evidence that looks at individual voters. Nonetheless, the result suggests voters may have been motivated to vote for Plaid Cymru to prevent Reform UK from winning the seat. This is, perhaps, the only crumb of comfort for Labour among the disappointment of a significant loss in an erstwhile heartland seat, as it is a dynamic the party hopes can be repeated elsewhere to its benefit.
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It is almost certainly too late for Labour to turn around its fortunes in Wales before the Senedd elections, and with those elections being held under a newly introduced PR system, it is not a dynamic that will be repeated in Wales in 2026. In this system, the only way to prevent Reform UK from gaining seats is to persuade people not to vote for the party, rather than consolidating the votes of those who wish to defeat it.
The system may be to Labour’s advantage: on current polling they will undoubtedly lose seats overall, but the impact may be less severe than it might have been had first-past-the-post elements been retained.
In the longer-term, Labour will be hoping the anti-Reform dynamic can be mobilised elsewhere for Westminster elections likely to be held in 2029. The challenge, of course, is that the electorate will need to be convinced that they are the best-placed (and most desirable) alternative to Reform UK in enough seats to hold on to power – while in England, the Liberal Democrats and the Green party will be challenging that position, Plaid Cymru has already staked its claim in Wales.
