Just under eight miles as the crow flies from the Welsh Parliament in Cardiff Bay, sits Caerphilly. Known typically for its vast castle – as Wales’ largest, and only second in the whole of Britain to Windsor – it has gained a new political relevance over the past couple of months. The valley town has become the backdrop for a by-election which itself is atypical.

The stakes in this by-election are high, with the winner potentially diminishing Labour’s control in the Senedd, and the election being an early indicator of the changing political climate in wider Welsh and UK politics. Yet, it has often been described as the “election that no one wanted.” Caerphilly’s by-election was triggered by the tragic loss of constituency MS, Hefin David, who was found dead in his home in mid-August, the day before his 48th birthday. A declaration followed for a by-election to take place, and at the time of writing, we have arrived at the day itself – Thursday 23rd October.

Candidate selections have trickled in, with the candidates finalised by the end of September. While candidates were put forward by eight parties, including the Liberal Democrats, Green Party, UKIP and Gwlad, the parties worth taking focus on from the polls are the remaining four. An interest by pollsters has sparked in Labour and the Conservatives.

Not because they are believed to have a chance, but for the damning decline these parties face. What once was believed to be the two immoveable forces of the two-party system in UK politics, are now mere distant bystanders according to opinion polling. Polling for this by-election puts Welsh Labour behind now at a mere 12%.

While the Tories aren’t known for success in Caerphilly, their position is a similarly ruinous one, falling to fourth place at 4%. To contextualise how significant this is – Caerphilly has always elected a Labour politician, ever since the birth of the Welsh Assembly (now the Senedd) in 1999. Not only that, but the late Hefin David won the seat in the last Senedd election in 2021 with nearly half the vote.

In place of Wales’ Labour-Tory duopoly, according to the most recent polls, rise Plaid Cymru and Reform UK. Currently, the two dominate the Welsh polls. The by-election is expected to echo this, placing Reform at 42% and Plaid at 38% of the vote.

This two-horse race materialises in the fight the parties are putting into Caerphilly. Plaid Cymru have been out on the doorstep. Their candidate, Lindsay Whittle, has been described in the local press as ‘Mr.

Caerphilly’. Reform UK, and their candidate Llŷr Powell, have even opened their own campaign headquarters for the by-election. It occupies what once was a phone shop on one of Caerphilly town’s main shopping streets.

The by-election has not been without controversy however for Reform UK. Their candidate was pulled into criticism after the former Reform leader in Wales was found guilty of taking Russia-linked bribes. Powell worked for the MEP at the centre of the scandal, Nathan Gill, up until December 2017.

Will the century-old Plaid Cymru be beaten by Reform UK?

The reason parties are committed to Caerphilly is the political context. For a majority in the Senedd, a party requires 31 seats. Most recently, Labour managed to maintain this vital 31 by their own 30 MSs, plus striking a deal with the lone Liberal Democrat Jane Dodds.

If Labour lose the Caerphilly seat, it leaves them with 29 of their own Members of the Senedd, meaning they must reconsider how they meet that 31- seat threshold. This is particularly vital for the Welsh government budget. If Labour can’t manage deals with two MSes in addition to their 29 MSes, they won’t be able to pass their spending plans.

In order to pass them, they will likely have to make concessions with other party politicians. Failing to pass a budget would enable automatic cuts under devolved law where only 75% of the budget can be spent, which could ultimately lead to vital cuts to local services and redundancies according to Welsh Labour politicians. Of equal importantance is the 2026 Senedd Election on the horizon, the optics of supporting the budget of a party in decline in the polls may not be considered desirable for competing parties ahead of that election.

This makes the Caerphilly seat rich in soft political power, and the by-election high stakes. Outside of Welsh politics, onlookers across the UK will also view this by-election closely to fathom whether Reform are truly dominating to the extent reflected in the polls, and whether Labour and the Tories are truly a distant memory. Will the century-old Plaid Cymru be beaten by Reform UK, a party still in its infancy?

From here, Caerphilly decides, and it’s those residents who will determine part of Wales’ future.