The political landscape of Caerphilly, a Welsh constituency long considered a Labour stronghold, underwent a seismic shift on October 23, 2025, when Plaid Cymru’s Lindsay Whittle clinched victory in a Senedd by-election. Whittle’s win, with 47.38% of the vote and 15,691 ballots cast in his favor, shattered over a century of Labour dominance and left many observers—and party insiders—scrambling to explain the result. Reform UK’s Llŷr Powell came in second, securing 12,113 votes (35.9%), while Labour’s Richard Tunnicliffe trailed in third with just 3,713 votes (11%). The by-election, triggered by the sudden death of Labour MS Hefin David, marked the first time in more than 100 years that Labour failed to hold the seat.
The turnout was remarkable by Welsh standards, reaching 50.4%—the highest ever for a Senedd by-election in Caerphilly and a significant jump from the 44% recorded in the 2021 election. According to The Conversation, this surge in participation was a clear sign that voters were highly motivated, not only by local issues but also by a broader national narrative that framed the contest as a pivotal test for the rising Reform UK party.
But what drove this historic upset? Labour insiders and political analysts alike have pointed to a confluence of factors: unpopular government policies, tactical voting, and a wave of discontent with both the Welsh and UK Labour leadership. Swansea East MS Mike Hedges, writing in an analysis for Labour Hub, was candid in his assessment. "The Westminster government became very unpopular very quickly. The decision to cut the winter fuel allowance for everyone who was not on pension credits was very unpopular and wrong," Hedges wrote. He further criticized the failed attempt at changing benefits, noting it "further weakened support."
Hedges didn’t mince words about the party’s leadership either. "The mention of [Prime Minister] Sir Keir Starmer’s name provokes derision including from Labour supporters," he observed, highlighting a sense of alienation and frustration among the party’s base. Local Welsh Government policies didn’t escape scrutiny, with Hedges citing the 20mph speed limit and the proposal to expand the Senedd as measures that "had put off voters in Caerphilly."
Beyond policy missteps, the Labour-run Caerphilly Council’s controversial plan to close libraries—an attempt to plug a £29 million budget gap—sparked public outrage. The proposals were paused in August following a legal challenge and backlash, but the damage to Labour’s reputation was done. Days after Labour launched its by-election campaign, the council leader, Sean Morgan, resigned and threw his support behind Plaid Cymru’s candidate, further undermining Labour’s efforts. Hedges summed up the local mood: "Caerphilly has locally been an unpopular Labour run Council. The library closure programme is both unpopular and unlikely to save substantial sums of money."
Yet, perhaps the most decisive factor in Plaid Cymru’s victory was the strategic behavior of voters determined to block Reform UK. Pre-election polls, including one by Survation, showed Reform leading Plaid, raising alarm bells among those opposed to the right-populist party. As reported by The Conversation and echoed by the BBC, there were “extraordinary stories” of habitual Conservative voters lending their support to Plaid Cymru in a bid to keep Reform at bay. The Conservative vote collapsed to fewer than 700, while the Liberal Democrats and Greens each took only about 1.5% of the vote—evidence that tactical voting was in full swing.
Hedges described the phenomenon succinctly: "This fed the ‘vote Plaid Cymru to stop Reform’ strapline being promoted by Plaid Cymru and led to a catastrophic drop in the Labour vote. This is a classic example of tactical voting, also of producing a self-fulfilling prophecy." On polling day, Labour canvassers reportedly encountered former supporters apologizing for their switch, explaining, "sorry, but I want to stop Reform, so I am voting Plaid Cymru."
Reform UK, for its part, invested heavily in the campaign. Senior figures, including Nigel Farage, made repeated visits to Caerphilly, and pre-election expectations were high. The party’s ultimate 36% vote share reflected its growing appeal among disaffected working-class voters and those frustrated with the status quo. However, as The Conversation noted, the result also exposed the party’s vulnerabilities: "Reform failed to convert intensive campaigning into victory." Polls suggest as many as 60% of voters are opposed to Farage as prime minister, providing an opening for opponents to unite behind more broadly acceptable candidates.
Labour’s collapse in Caerphilly is emblematic of broader challenges facing the party across Wales and the UK. The Socialist Party, which campaigned against library closures in the constituency, pointed to persistent poverty, deindustrialization, and 15 years of austerity as underlying causes of voter discontent. "The experience of over a year of a Starmer’s Labour government has evaporated the idea of Labour being a ‘lesser evil’. ‘Worse than the Tories’, is how they have been described by many approaching our Socialist Party campaign stalls," wrote Geraint Thomas in a post-election analysis.
Looking ahead, the Caerphilly by-election offers both a blueprint and a warning for parties seeking to counter Reform UK’s national surge. As The Conversation observed, "Harnessing this anti-Reform majority, however, requires a level of co-ordination rarely seen in the UK’s electoral history." The fragmented opposition—split among Labour, Liberal Democrats, Greens, nationalists, independents, and even some Conservatives—briefly coalesced in Caerphilly, driven by a clear polling trigger and a high-stakes media narrative. The challenge will be replicating this unity in future contests, especially as Wales prepares for the May 2026 devolved elections, which will use a proportional voting system.
For Plaid Cymru, Lindsay Whittle’s win is both a historic achievement and a testament to the power of local roots and a progressive message. For Labour, the result is a wake-up call—one that underscores the need to reconnect with disaffected voters and address grievances both local and national. And for Reform UK, the by-election is a reminder that momentum alone is not enough; overcoming tactical voting and building a broad base of support will be essential if it hopes to convert popularity into seats.
The Caerphilly by-election may have been just one contest, but its reverberations are likely to be felt far beyond the valleys of South Wales, offering lessons—and warnings—for the political battles yet to come.
