In a stunning political upset, Sir Keir Starmer’s Labour Party has lost the Caerphilly seat — a constituency it had held for more than a century — to Plaid Cymru, marking a seismic shift in Welsh politics and delivering a major blow to Labour’s leadership ahead of key elections in May.
The by-election result saw Plaid Cymru’s Lindsay Whittle secure victory with a majority of 3,848 votes, capturing 47% of the vote (15,961 ballots) and overturning Labour’s long-standing dominance in the South Wales heartland. Reform UK’s Llŷr Powell came second with 36% (12,113 votes), while Labour’s Richard Tunnicliffe suffered a devastating collapse, taking just 11% (3,713 votes), down sharply from 13,289 votes in 2021.
The Conservative candidate Gareth Potter trailed far behind with only 690 votes (2%), while turnout reached 50.43% — the highest ever recorded in a Welsh Assembly by-election.
A Century-Old Stronghold Falls
Labour’s defeat in Caerphilly — both a Westminster and Senedd stronghold since the early 20th century — represents one of the most symbolic political losses in Wales’ modern history.
Whittle, a veteran campaigner who had previously failed in 13 attempts to win the seat, hailed the result as the beginning of a new political era for Wales.
“We want a better deal for every corner of Wales,” he declared in his victory speech. “The big parties need to sit up and take notice. We are at the dawn of new leadership — a new beginning.”
Whittle, who served as a regional assembly member for South East Wales from 2011 to 2016, becomes Plaid Cymru’s 13th representative in the 60-member Senedd. His win reduces Labour’s count to 28 seats, stripping the party of its working majority.
Labour’s Decline and Internal Strains
The defeat comes amid growing disillusionment with Labour in Wales, exacerbated by the resignation of former First Minister Vaughan Gething following a donations scandal.
Current Welsh First Minister Baroness Eluned Morgan acknowledged the public’s frustration, saying Labour “has heard the message from Caerphilly that change hasn’t come quickly enough.”
However, Deputy First Minister Huw Irranca-Davies insisted the party would recover:
“To paraphrase Mark Twain — rumours about our death are greatly exaggerated,” he said.
Political analysts have pointed to Labour’s perceived shift to the right on issues such as immigration and crime as a factor alienating parts of its traditional base and creating space for both Plaid Cymru and Reform UK to attract protest votes.
Reform’s Rise and Plaid’s Tactical Advantage
The result also underscored the growing influence of Nigel Farage’s Reform UK, which had entered the race as the bookmakers’ favourite after leading in a local poll. Farage visited the constituency three times during the campaign, underscoring the party’s ambitions in Wales.
While Reform ultimately fell short, the 36% it captured marked a major advance for the party and confirmed its appeal among voters frustrated with mainstream politics.
Analysts say tactical voting likely helped Plaid Cymru clinch victory. Luke Tryl, director of More in Common, said left-leaning voters rallied around Plaid to block Reform, noting “minimal support” for the Greens or Liberal Democrats.
Plaid leader Rhun ap Iorwerth agreed, saying, “There was clearly an element of voters wanting to stop Reform.”
Implications for UK and Welsh Politics
The Caerphilly result has significant implications for both Labour and Prime Minister Keir Starmer, who faces increasing pressure ahead of the May 2026 Senedd elections and future UK-wide contests.
Losing a seat that Labour had held for over 100 years will fuel doubts about Starmer’s ability to retain traditional working-class support, particularly in devolved regions where local identity and nationalist sentiment remain strong.
The outcome also weakens Labour’s position in the Senedd, forcing it to rely on support from Plaid Cymru, the Liberal Democrats, or independent members to pass legislation.
Meanwhile, Reform UK’s strong showing will concern both Labour and the Conservatives, signaling a realignment in Welsh politics. Reform’s head of policy Zia Yusuf called the result “remarkable,” predicting that “the Senedd elections next May are now a battle between Reform and Plaid.”
A Warning for Starmer and Beyond
Though Labour leaders have downplayed the significance of the by-election as a local anomaly, political observers argue that the loss exposes deeper vulnerabilities.
As Plaid Cymru celebrates its landmark victory, the result sends a clear message: Welsh voters — long loyal to Labour — are increasingly willing to embrace new voices promising local accountability and change.
The by-election, as one analyst noted, “is not just about Caerphilly — it’s a warning shot to Labour across the UK.”
