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By Thomas Lockwood, York St John University

Plaid Cymru’s overwhelming victory in the recent Caerphilly Senedd by-election shattered over a century of political tradition. Lindsay Whittle took the seat with 15,691 votes. Labour, which had held the seat since it was created, came away with just 3,713 votes.

Reform came second to Plaid, with 12,113 votes. And while this was an impressive performance, the fact that it failed to win Caerphilly even after vast amounts of time and money spent on the campaign has led to speculation that tactical voting played a part in this by-election.

A big clue that tactical voting was at work in Caerphilly was the recorded turnout. Typically, by-elections in Wales have been low-key affairs. Turnouts are low and incumbents generally win. The national average for a Senedd vote in a constituency has never tipped over 50%. In Caerphilly, turnout climbed from 44% in the 2021 election to 50.4% in this by-election.

And while local voters clearly backed Plaid Cymru for plenty of reasons, the extremely low vote count for other parties does suggest at least some lent their vote to Plaid to keep out Reform. The Conservative vote collapsed to fewer than 700 votes and the Lib Dems and Greens, so often the recipients of tactical votes themselves, each took just 1.5% of the votes in Caerphilly.

Anecdotes from the vote count support this. The BBC recounted “extraordinary stories” of habitual supporters of the Conservatives, a pro-union party, voting Plaid to block Reform.

The increased turnout and Plaid’s 27.4% swing both suggest a mobilisation, triggered by polling and a wider national narrative which persuasively contends that Reform is ahead of other parties. Does the result therefore imply that Reform can be beaten elsewhere if voters take the right approach to tactical voting?

The limits of Reform’s surge

Reform entered the Caerphilly race with no prior foothold in the constituency. The party mobilised heavily and, it had seemed, effectively. Nigel Farage and other senior Reform figures made multiple visits to the area to campaign for their candidate, Llŷr Powell. Pre-election polls, including one by Survation which had Reform leading Plaid by 42% to 38%, raised expectations of a breakthrough.

And it is true that Reform’s ultimate 36% vote share reflects its growing appeal among disaffected working-class voters. It did capitalise on the same anti-establishment sentiment that has seen the party top UK-wide polls for much of the past year.

Yet, the result also exposes Reform’s vulnerabilities. As with the Hamilton, Larkhall and Stonehouse by-election for the Scottish parliament earlier in the summer, Reform failed to convert intensive campaigning into victory.

The role and reach of tactical voting

Underneath the hype, Farage is unpopular. Polls suggest as many as 60% of voters are opposed to him being prime minister. That presents an opportunity for opponents to unite behind a more broadly acceptable candidate.

In this volatile political era, where voters show little loyalty to tradition, smaller parties like Plaid Cymru, the SNP, Greens and even Pro-Gaza independents could frame themselves as the “real alternative” to Reform. Depending on local dynamics, they could attempt to draw tactical support.

It should be noted, however, that tactical voting cuts both ways. While it denied Reform a victory in Caerphilly, the party could attract tactical support from Conservative voters eager to oust Labour governments.

In England, without equivalents to Plaid or the SNP to siphon anti-establishment sentiment, Reform may consolidate its grip on working-class disillusionment. This trend was evident in Labour’s collapse in the Runcorn and Helsby Westminster by-election in May 2025, which enabled Reform to take the seat.

In Caerphilly, Labour’s vote fell amid grievances including the slow pace of change to improve living standards, policy u-turns and a fatigue with Welsh Labour, which has been in power in the Senedd since its creation in 1999.

Such grievances can be felt across the UK more broadly – with winter-fuel policy u-turns, and a general dissatisfaction with how long it is taking Labour to deliver on promises to improve living standards. Concern about immigration is also used to punish Labour in both the regular voting intention polls and at the ballot box in council by-elections.

An anti-Reform majority does exist – and it has shown up in several contests, including in races Reform has ultimately won but on less than 50% of the vote. Harnessing this anti-Reform majority, however, requires a level of co-ordination rarely seen in the UK’s electoral history.

Unlike the 1997 anti-Conservative wave, there is no single opposition brand. Instead, the anti-Reform vote is split across Labour, Liberal Democrats, Greens, nationalists and independents – and, arguably, the Conservatives too.

In Caerphilly, we saw this fragmentation briefly turn into coalescence. This implies that a clear polling trigger, showing Reform ahead in a seat, can focus the minds of voters and drive tactical thinking. It also helped that these voters were offered a Plaid candidate with deep community roots and a strong, progressive message.

What is potentially harder in a general election is the presentation of a local contest as extremely high stakes in the media. Caerphilly drew unprecedented attention precisely because it was being framed as a test case for Reform in Wales, which may explain the level of anti-Reform vote.

In a multi-polar UK, the anti-Reform majority is real – but not pro-any one party by default. Importantly, it is anti-populist, anti-incumbent and regionally variable. Nearly all of the mainstream parties on the centre ground and left wing of politics are claiming to be the real alternative to Reform.

Reform’s path to power lies in building a lead that is too large for tactical voting to overcome, or in electoral systems which reward vote share over seat efficiency. This is why it remains hopeful of success in May 2026 in Wales, where the election is being held under a proportional voting system.

As the UK heads towards the 2026 devolved elections and a likely 2029-30 general election, Caerphilly offers a blueprint for resistance to Reform’s national surge. It also offers a warning for the other parties: stopping Reform is not the same as winning.

Thomas Lockwood, PhD Researcher in Politics, York St John University

This article is republished from The Conversation under a Creative Commons license. Read the original article.