Starmer must tread Caerphilly after by-election disaster

Sir Keir Starmer has endured several by-election routs during his first 18 months as Prime Minister, but none as bruising as Caerphilly.

Labour’s vote share collapsed by 35 points in what had been one of its safest Welsh seats, handing victory to Plaid Cymru and ending more than a century of uninterrupted Labour representation in the area. Just 3,700 voters backed the Labour candidate - scarcely more than friends and family - underscoring the scale of disengagement among even the party’s most loyal supporters.

While caution is always needed when extrapolating from a single contest, the Caerphilly result is nevertheless telling. It confirms that the government’s standing has been eroded not only in marginal constituencies but in the party’s historic heartlands too. Many of those who once saw Labour as the default choice have either abandoned the party entirely or are willing to vote tactically for others. That pattern will further unsettle many of Labour’s 2024 intake navigating shallow majorities.

For Reform UK, which finished a close second with 36 per cent of the vote, the contest was both a missed opportunity and a validation. Despite falling short of victory, the party demonstrated genuine reach beyond its English heartlands, outpacing even UKIP’s high-water mark there in 2010 by 14 points. Nigel Farage’s message is clearly resonating with parts of the electorate that once formed Labour’s core coalition. However, the result also underlines a structural challenge for the populist party: in first-past-the-post contests, tactical voting among left-leaning voters could still act as a brake on their ambitions and may become a prominent talking point in May’s devolved elections.

The literal winners were Plaid Cymru, who overturned a massive Labour majority and in doing so shifted the political narrative in Wales. Beyond the immediate result, the party will take encouragement ahead of next year’s Senedd elections. Having long played second fiddle to Labour, Plaid now has a plausible claim to be the devolved government in waiting.

But the ramifications extend well beyond Wales. Labour’s collapse in Caerphilly will alarm Scottish Labour leader Anas Sarwar, who faces his own fight to re-establish Labour’s dominance north of the border. A perception that nationalist movements are again gaining ground could prove particularly corrosive.

Most significantly, the result compounds the sense of drift around Starmer’s premiership. Discontent has been simmering on the Labour backbenches since the summer, with many MPs increasingly doubting their leader’s strategy and ability. Caerphilly will almost certainly not in itself trigger a leadership challenge - but it reinforces a gathering narrative that this is a leader, and perhaps even a government, operating on borrowed time.