Reform UK’s by-election defeat at the hands of Plaid Cymru exposed a “very real obstacle” for Nigel Farage, a polling guru has claimed.

Lindsay Whittle secured 15,961 votes in yesterday’s Caerphilly by-election, nudging him ahead of Reform UK’s Llyr Powell on 12,113.

Despite being neck-and-neck throughout the Senedd by-election campaign, Reform UK appeared to fall agonisingly short as progressive voters coalesced around Plaid Cymru to prevent Mr Farage claiming victory.

Support for Labour, who first won the seat in 1918, collapsed to a mere 3,713 votes.

Merlin Strategy founder Scarlett Maguire suggested that a so-called “Stop Farage” alliance played a pivotal role in preventing Reform UK from claiming its first major victory in Wales.

Ms Maguire told GB News: “The Caerphilly by-election shows the potential for a progressive stop-Farage coalition that Reform should be taking seriously.

“It could be harder to replicate in a proportional representation system, but also presents a very real obstacle for the party.

“They are also going to need to come up with better answers on topics outside of immigration, particularly the NHS and the economy.”

Mr Farage appeared to admit that even Reform UK was surprised at the level of support for Plaid Cymru.

“At the start of polling day, I thought that we would get 12,000 votes and we did,” the Reform UK leader said.

“I thought that number would be enough, but it wasn’t. The total collapse of the Labour vote to Plaid was to a party that people know well and to a popular local politician.”

During the Caerphilly campaign, GB News was told by Reform UK insiders that attacks from both Labour and Plaid Cymru on the NHS had cut through with voters on the doors.

Decade-old comments by Mr Farage had been plastered on anti-Reform UK attack adverts, including ones calling for an insurance-based health system.”

“It’s been a vicious little campaign by the left,” an insider said last week.

Labour had even been forced to pull one of its attack adverts against Mr Powell after it attempted to connect him with former Brexit Party MEP Nathan Gill.

Gill, who employed Mr Powell as a caseworker in the EU Parliament, pleaded guilty last month to taking bribes from Russia.

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Despite the by-election blow, Ms Maguire also pointed out that Reform UK performed in line with expectations.

“They did not underperform their Welsh national polling, which shows that the appetite polling has been showing for Reform from a chunk of the Welsh population is real,” Ms Maguire told GB News.

Next year’s Welsh Parliament Election will not bring up the same electoral challenge that Reform UK faced this morning.

All 40 constituency seats are set to be abolished before May 1, being replaced by 96 party-list contests across 16 super-constituencies.

Last night’s result would likely see Plaid Cymru and Reform UK pick up three seats each in Blaenau Gwent Caerffili Rhymni, leaving Labour with zero MSs in the once-safe stronghold.

However, tactical voting could bring about challenges for Reform UK in Wales at the next General Election.

Reform UK is currently ahead in 22 constituencies in Wales, polling aggregator Election Maps has claimed.

Plaid Cymru looks poised to pick up six seats, with Labour securing just two and the Tories and Liberal Democrats winning just one seat respectively.

But Reform UK’s support remains very shallow in a number of key targets.

Election Maps places Reform UK 3.6 per cent ahead of Plaid Cymru in Caerphilly’s Westminster seat.

However, the anti-Reform UK support could quickly restore Plaid Cymru’s advantage, with 19 per cent currently backing Labour, 7.1 per cent supporting the Green Party and 6.5 per cent siding with the Liberal Democrats.

It is a similar story in the Gower, where 30.2 per cent of voters would currently vote for Reform UK – just 6.7 per cent ahead of Labour – but support for Plaid Cymru, the Green Party and Liberal Democrats sits at 32.7 per cent.