Reform holds 11% lead over Plaid Cymru in Westminster election poll, as centre left vote fragments in Wales

Martin Shipton

Reform UK has an 11 point lead over Plaid Cymru in the latest YouGov/Cardiff University opinion poll for Westminster voting intentions, as centre-left support becomes increasingly fragmented across multiple parties amid an increase in support for the Greens.

The latest poll conducted by YouGov for Cardiff University shows Reform UK at 30%, while opposition votes are split between Plaid Cymru (19%), Labour (15%), the Greens (14%) and the Liberal Democrats (8%). Conservative support remains squeezed at 13%.

Unlike Senedd polling which shows consolidation behind Plaid Cymru – which holds a three-point lead of 33% to 30% over Reform in the latest poll – Westminster voting intentions reveal fragmentation on the left and consolidation on the right – a pattern that if replicated at the next Westminster election could have important implications for seats won under First Past the Post.

A joint post by Dr Jac Larner and Dr Ed Gareth Poole (both of Cardiff University) states: “Between November 28 and December 10 we surveyed approximately 2,500 adults in Wales online via YouGov. This is separate to ITV Wales’ Barn Cymru polls and does not use YouGov’s MRP weighting method.

“The headline figure for Reform UK is in line with previous polling; but the parties on the left are now more fragmented, with a notable increase in Green party support.

“This evidence closely aligns with other Wales and UK-wide Westminster voting intention data which show a dramatic shift in the political landscape; one which has now been sustained for many months.”

The blog displays how individual respondents report they will vote in the next Senedd election vs a hypothetical Westminster election. It states: “The patterns are striking, with substantial portions of the electorate reporting different voting intentions at different levels.

“In our accompanying analysis of Senedd voting intentions, we saw a story of consolidation rather than fragmentation. That blog introduced an analytic lens based on two distinct coalitional blocs that operate in Welsh politics, ones which are structured primarily by national identity. Within the ‘Welsh/Left bloc’ (Labour, Plaid Cymru, and Greens), we saw progressive, Welsh-identifying voters moving from Labour towards Plaid Cymru. Within the British/Right bloc” (Conservatives, UKIP/Brexit Party/Reform UK, and Abolish), we witnessed conservative, British-identifying voters shifting from the Conservatives to Reform
UK. We interpreted this as a kind of a sorting process, where voters appeared to be consolidating around the strongest apparent option within each ideological grouping.

“Reform UK demonstrates a solid lead within a consolidated British/Right bloc, benefitting from Conservative support squeezed at just 13%. The Welsh/Left bloc, however, splits opposition votes across multiple parties: Plaid Cymru (19%), Labour (15%), and Greens(14%). Relative to the September ITV Wales/YouGov data (which uses a different method), The Greens have doubled their support from 7% to 14%.

“Unlike the Senedd’s new voting system, which is based on an (albeit imperfect) version of List Proportional Representation, if this story of British/Right consolidation and Welsh/Left fragmentation were repeated it would be intensified by Britain’s First Past the Post electoral system. Under FPTP, a party can win a constituency with well under 30% of the vote if opposition support is sufficiently divided.

Assuming Reform UK’s support is distributed relatively evenly, on a uniform swing virtually every seat in Wales could be competitive for the party. A 30% vote share, if efficiently spread, could translate into a disproportionately large number of seats when facing three or four divided opponents.

“For voters opposed to Reform UK, tactical voting represents the most obvious counterstrategy – one of the explanations for the lopsided result in the Caerphilly byelection (which used FPTP). But to be effective, tactical voting requires clear information: voters must know which party has the best chance of defeating Reform UK in their own constituency.

“This is where the current polling data reveals a critical problem. Unlike in Senedd elections, where Plaid has always outperformed its Westminster results, the Westminster picture is murkier. Does incumbent Labour remain the main challenger to Reform UK in the valleys, or has Plaid Cymru taken over that mantle post-Caerphilly? Are the Greens now competitive enough in urban seats to provide a vehicle for anti-Reform tactical voting? At present, voters lack the constituency-level data needed to make these
calculations effectively.

“This informational deficit contrasts sharply with the Senedd context, where evidence of consolidation behind Plaid Cymru appears to imply that strategic voting decisions are more straightforward. The fragmentation in Westminster voting intentions creates not just a mathematical problem for Reform’s opponents, but a coordination problem that may prove difficult to resolve before the next general election.

“The polling suggests that at the next Westminster election, in the absence of voter consolidation into one dominant centre-left party or highly effective tactical voting coordination, Reform UK could achieve breakthrough results in Wales. Parties on the centre-left face a core challenge: how to somehow signal to voters that their party represents the strongest challenge to Reform UK in each constituency. How this coordination problem is resolved – or whether it can be resolved at all – may determine the electoral map of Wales for years to come.”

While this new poll was not an MRP poll, which enables reasonably accurate projections of results to be made on a constituency basis, such a poll was carried out by YouGov in September 2025. It showed Nigel Farage on course to be Prime Minister, with Reform UK performing better in Wales than in most English regions.

The party would have won 23 of the 32 seats in Wales at a general election, with six going to Plaid Cymru and just three for Labour.

The Conservatives and Liberal Democrats would have won no seats. Plaid would have won its existing four – Caerfyrddin, Ceredigion, Dwyfor Meirionnydd and Ynys Mon – plus Bangor Aberconwy and Cardiff West.

Labour would have won the other three seats in the capital: Cardiff East, Cardiff North and Cardiff South and Penarth.The YouGov MRP polling projection, based on a 13,000 sample taken over three weeks, suggested an election would have seen a hung parliament with Reform UK winning 311 of the 650 seats, 15 seats short of the formal winning line of 326.

In practice, once the Speaker and absent Sinn Fein MPs were accounted for, it would be all but impossible for anyone other than Mr Farage to secure the largest number of MP backers and thus become Prime Minister.