What does the Caerphilly by-election tell us about the state of Welsh politics? – Inside track

Last week, a by-election in Caerphilly in South Wales was won by Plaid Cymru. With elections to Senedd Cymru – the Welsh Parliament – just seven months away, this result highlights the political uncertainty and choices facing Wales, as the long-held dominance of the Labour party appears to be slipping away.

The by-election had been predicted to be a two horse race between Plaid Cymru and Reform, despite Labour having held this Senedd seat since its creation in 1999 and the corresponding Westminster constituency for over a century. This turned out to be the case, with Plaid Cymru winning with 47 per cent, Reform coming in second place with 36 per cent and Labour’s vote collapsing to 11 per cent. Turnout in Caerphilly was much higher than usual at over 50 per cent, suggesting people were keener to vote than usual.

Lindsay Whittle, the successful candidate, had tried to win the seat 13 times before, proving that sometimes the Welsh proverb “Dyfal donc a dyr y garreg” (which translates as “tapping persistently breaks the stone”) can be a route to electoral success.

The Caerphilly result is not surprising given the direction of travel predicted by recent polling. I grew up in a South Wales valley town which used to have the biggest Labour majority in the UK. My Mum used to quip that it didn’t matter who Labour pinned their rosette on, come election day they’d win regardless. Those days of electoral predictability appear to be over.

Keir Starmer said he was “deeply disappointed”. But some political commentators have argued there’s a silver lining: despite Reform pouring significant resources and political capital into the seat, voters ultimately backed a centre-left progressive party instead. Meanwhile, Welsh First Minister Eluned Morgan has sought to increasingly distance Welsh Labour from its UK counterpart and notably gave one of the most left leaning speeches at the Labour party conference in Liverpool, which could see the paths of Wales and Westminster further diverge.

How will the new electoral system in Wales work? To compound uncertainty, the May 2026 Senedd elections will be run using a new closed proportional list system and the D’Hondt formula which is intended to better represent voters’ choices across Wales as the number of seats a party or independent candidate wins will more closely reflect the percentage of votes they get.

The Senedd is set to increase from 60 to 96 members, with 16 constituencies each electing 6 representatives. Parties can list up to eight candidates per constituency, and independent candidates may also stand for election. Seats will be allocated based on the share of votes each party or independent candidate gets. For example, if a party wins three seats, the top three people on their list will be elected to those seats.

It means the seats towards the bottom of the lists could end up being highly contested. Anyone getting under around twelve per cent as Labour did in their former stronghold of Caerphilly will be unlikely to get a seat. The ‘sixth seat’ in each constituency could be very difficult to predict and decided by the slimmest of margins.

Coalition working is inevitable, including on the environment

Whatever the election result it is hard to imagine an outcome in which the formation and operation of the next Welsh government do not entail some form of coalition working. This isn’t new in Wales. While Labour has always led the Welsh government, it has previously formed a coalition with the Lib Dems, agreed a shared programme of work with Plaid Cymru through the Cooperation Agreement and relied on Jane Dodds, the only Lib Dem in the current Senedd, for support to pass its budget.

More such collaboration will be needed in the short term as the Caerphilly result means that Labour now holds 29 rather than 30 seats of the 60 member Senedd. It will need support from another party as well as Jane Dodds to pass budgets or bills for the rest of this Senedd term.

This matters for the environment as a bill is currently passing through the Senedd to address the ‘governance gap’ in Wales created by Brexit, when the oversight that was provided by the European Commission and courts fell away.

That bill will also require the next Welsh government to take long overdue action to turn around the dire and declining state of nature in Wales, which has seen iconic species and habitats disappear at an alarming rate. It must pass before the end of this Senedd term and include a clear timetable for implementation, so that momentum on improving the environment is sustained beyond the May 2026 election.

Luckily, the bill is supported across the political spectrum, was a commitment of the cooperation agreement with Plaid Cymru and party manifestos, and has been called for repeatedly by members of the Senedd. A Senedd scrutiny committee, chaired by Plaid Cymru, has called for it to be strengthened, as have environmental organisations, the Future Generations Commissioner and legal experts. But given the unpredictable state of Welsh politics, the bill’s passage will need to be monitored closely to ensure that it passes in time and is not watered down.

With Plaid Cymru’s rise comes increased scrutiny of its policies and people. As with most parties, it has environmental champions, sceptics and fence sitters, and only time will tell whether it has the nature blind spot some fear. Reform’s plans will also be pored over, once they move on from headlines to policy detail. It is in the public interest for all parties to set out their environmental commitments ahead of what will be one of the most consequential elections in Wales since devolution.