The south Wales town of Caerphilly is known better for its vast, 13th century castle than its politics — but establishment parties might want to pay it a visit.
A century of rule by the center-left Labour Party was smashed to rubble Friday in a by-election for the Senedd, the Welsh parliament. Labour’s vote bled away in its oldest heartland to two rivals: Welsh nationalists Plaid Cymru on the left (47.4 percent) and Nigel Farage’s populist Reform UK on the right (36 percent).
Labour’s mere 11 percent is alarming strategists ahead of full elections to the Senedd in 2026, as well as a Westminster general election by 2029.
By-elections must be read with skepticism because they give voters a “free hit” on the ruling party.
And in many ways, this result was uniquely Welsh. Labour only regained Westminster in 2024 but here the party had all the trappings of incumbency, long running both the local council and Welsh government. Plaid’s specific support base for Senedd elections does not read across to Westminster. Welsh institutions including health and education are creaking. Welsh political rows (such as Labour’s 20mph road speed limits) were prominent.
Yet the result also has wider lessons for an establishment party fighting populists in a fractured age, facing both ways to two rivals each promising to restore pride in their country.
POLITICO looks at five takeaways that will resonate beyond the castle walls.
1) Watch out for the non-voters
Turnout on a wet October Thursday was 50.4 percent, Caerphilly’s highest ever in a Senedd election.
This was fueled in part by people who rarely vote choosing to back right-wing populists, argued strategists from Labour and Reform.
The phenomenon was not as great as Farage’s party hoped, and it met a greater surge of Plaid voters seeking to stop him. Even so, one Labour strategist — granted anonymity to speak freely, like others in this article — argued non-voters were “definitely” a factor in Reform’s support. They pointed to higher-than-usual turnouts in recent council by-elections where Reform has done well.
Gareth Beer, a Reform parliamentary candidate in 2024, recalled one interaction this week in Caerphilly: “This guy said he hadn’t voted for 26 years, and he’s going to vote for Reform now, just to give [Labour] a kick up the backside.”
This “poses a challenge for our traditional campaigning methods,” argued the Labour strategist quoted above. They added: “We’ve spent all these years farming data on people who we know vote, and are often inclined to vote Labour. Whereas these voters, because they don’t vote, our first instinct is we don’t bother. So we have no data on them.”
Polling by Survation, shared with POLITICO, indicates there might a similar pattern across the U.K., albeit less pronounced. In a September sample of around 1,200 people who did not vote in 2024, 27 percent said they would now back Reform — up from 8 percent a year earlier. Only 20 percent of them would vote Labour, down from 35 percent.
2) Tactical voting is a big deal
Plaid argued successfully that it — not Labour — was best placed to keep Reform out of power. “People have seen it’s a two-horse race and they’ve decided they have to vote tactically to stop Reform,” a Plaid Cymru strategist said on polling day.
Labour used unorthodox methods in a failed bid to swing voters the other way. A Labour leaflet circulated this week depicted Reform on 32 percent, Labour 28 and Plaid 19 with the headline: “Is it worth the risk?” Yet the small print admitted it was based on six-month-old modelling for the Westminster seat.
This speaks to an existential dilemma. Labour’s dominance has long made it the fallback option for voters who want to keep the Conservatives — or Reform — out of power. If Prime Minister Keir Starmer can no longer convince people of that, he is in deep trouble.
Ironically, this question of tactical voting matters least in Wales. This was likely the last Senedd election under the current system before a semi-proportional model launches next year.
But Westminster elections are still fought under “first past the post,” a winner-takes-all system where each seat has only one MP.
Tactical voting in a U.K. general election, where Labour is facing multiple fronts, will be far more unpredictable than Caerphilly. While Plaid is an “established receptacle for disaffected progressives,” according to the Labour strategist quoted above, the centrist and left-wing vote in England is split between Labour, the Liberal Democrats, the Green Party and a nascent party co-founded by former Labour leader Jeremy Corbyn.
3) Incumbency sucks
Labour knows the force of anti-incumbency in Britain, having run its 2024 campaign on a single word — “change.” That same word has now come back to bite Wales’ Labour establishment. The result suggests there are no safe havens where parties can count on historical support, and that parties that were until recently on the sidelines (Plaid and Reform) can hit the big time.
“Betrayal was the most common word we heard on the doorstep,” said one Reform aide.
Labour’s proposed solution is the same as it has been since summer 2024: “delivery.” Nick Thomas-Symonds, a ministerial ally of Starmer and Welsh historian of Labour, promised Friday to “redouble our efforts” on showing tangible change.
One Labour minister said: “We’ve got to start listening to people and delivering on the basics. Stop trying to be existential and be too big picture. That’s not going to cut it any more — people are fed up and disengaged and angry.”
This by-election result will make that harder in itself. Labour is two seats short of a Senedd majority, so will need opposition support to pass its budget in January.
The result might suggest the center cannot hold — but with caveats. Welsh Labour itself is not centrist, and has long been further to the left than U.K. Labour. Even so, the Labour strategist quoted above said: “We’re losing progressives to Plaid, and we’re losing post-industrial lower-middle class people who are sick of everything to Reform.”
The picture may be more positive for Labour in Scotland, where it is up against the incumbent Scottish National Party in May 2026 elections. One Labour official said: “The dynamics there are different … I think the thing that’s keeping Scottish Labour going is most people say they’re driven by whether or not the NHS runs. And they don’t think the SNP has done a good job of running public services in Scotland.”
4) Watch your messaging
Many internal Labour grumbles were about the party’s messaging.
Incumbency left Labour’s candidate Richard Tunnicliffe in an impossible position locally. His interventions included fighting library closures proposed by Caerphilly’s own Labour council.
By contrast, Reform and Plaid were able to score easy wins by campaigning on local and Welsh issues, such as the NHS, education and 20mph zones (Reform put up a striking billboard against the latter).
There was also frustration in Labour that Reform could talk up concerns about migration when the issue is not devolved to the Welsh government. But Beer said people’s concerns were justified: “They watch TV and they see what’s happening in the rest of the country.”
And the Labour strategist quoted above said: “We can’t just fight this fight with facts. It’s vibes. You can tell people that only 2.5 percent of people on Caerphilly are immigrants, but this isn’t how you fight that fight. There are still too many people who think that if people only knew the truth, they wouldn’t vote Reform. It’s not that simple.”
Some Labour figures raised eyebrows too about a social media strategy designed to appeal to 16- and 17-year-olds (who can vote in Senedd elections). This included a slow-motion TikTok clip portraying Labour’s candidate as sexy “daddy” and a low-fi polling day message that said “our graphic designer is on leave” and “pls vote welsh labour today x.”
A Labour Senedd member said there was “huge unhappiness in the Labour group at the way the campaign has been run — not we that thought we could do well, but for making us look like idiots.”
5) Nothing sticks to the populists … yet
Plaid and Labour both had a gift handed to them mid-campaign. Reform’s former leader in Wales, Nathan Gill, pleaded guilty in September to taking bribes to make statements in favor of Russia while being a Member of the European Parliament.
Yet there was disagreement between activists who spoke to POLITICO about how much it had come up on the doorstep, if at all. One Welsh Labour strategist argued the issue did cut through to voters, but “whether it cut through to the extent where it makes a massive difference I don’t know.”
This speaks to a wider question troubling Labour strategists (and pleasing Reform aides) in Westminster — whether any attack can stick to Farage’s outfit.
“You might say we’re a bit Teflon,” Beer accepted. “But the general public are not interested in petty squabbling and the kind of stuff we get stuck in the weeds about, the tittle tattle. They just want to get the country fixed.”
There is a silver lining for Labour, though.
Reform’s performance in Caerphilly was worse than a Survation poll last week predicted. The 11-point gap with Plaid was far wider than expected. And the party is now grappling with a delivery problem of its own, planning tax rises in councils where it won control in England.
Reform might — just — be starting to see where the ceiling lies on its support. Or at least, that’s what its rivals will fervently hope.
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