Welsh Senedd Election Odds: Has Reform's Bubble Burst?

By-elections tend to fall into three categories. First, the forgettable, predictable races which merely confirm a trend. 

Second, races which demonstrate a clear change in the political weather. 

Third, ones that not only change the weather, but are exciting, close and unpredictable - on betting sites too.

Caerphilly belongs in the third box. Plaid Cymru, the outsiders, won as earmarked on these pages last week. 

On polling day, they drifted out to as big as 6/1, before winning by a comfortable 11% margin, but this was more than just a betting upset. 

It was a critical straw in the wind as to where Welsh and UK politics may be heading during an unstable, transformative period in history. There are ramifications for various longer term betting markets.

First and foremost, Labour’s performance was predictably disastrous. They lost three-quarters of their vote. 

Welsh Senedd Election Odds:

(Odds correct at time of publish: 4.30pm - 27/10/2025)

If this is repeated at May’s elections to the Welsh Senedd, they could end up losing all or certainly most of their seats (they currently hold 30, half of the 60 in total).

The party could soon find themselves locked in an existential crisis in the same manner that the Conservatives have in recent years. 

The duopoly which has dominated UK politics for a century has collapsed. These trends in Wales are reminiscent of Scotland following their 2014 independence referendum. 

At the 2015 general election, Labour lost all but one of their 41 seats. The Scottish Nationalists won the lot.

Senedd Betting Is Tightening

Their Welsh equivalent isn’t about to replicate that success for various reasons, from the much lesser demand for independence to linguistic divide, but they are in a very strong position for next May. 

Reform remain favourites to win the most seats in the Senedd, at a best-priced 5/6 on betting apps, but Plaid Cymru are closing fast at 11/10.

Taking odds-on about Reform makes very little appeal after Caerphilly. If Labour were the big losers, Reform are a close second. 

Everything was in place for a big, momentum-building win. They poured resources in. They continued to enjoy blanket media coverage.

The Conservative vote completely collapsed to 2%, overwhelmingly in their favour. Yet they only scored 36%, in a constituency where the demographics were highly suitable to their insurgent movement.

What happened? Well, Nigel Farage says he thought the 12,000 votes they won would be enough. 

This makes sense, if turnout was low as it usually is in by-elections. But in fact, turnout topped 50% - outstanding in these circumstances. 

Turnout and enthusiasm to vote are always absolutely critical to determining and indeed betting on elections. Reform’s well-funded machine failed on that score.

Farage Remains The Marmite Candidate

In addition, this result supports the theory that Reform have a low ceiling and are largely toxic to non-supporters. 

This was the case with Farage’s first party, UKIP. The issue which defined his career, Brexit, now has clear and dwindling minority support. 

Whilst their divisive, even incendiary rhetoric on immigration certainly appeals to a large chunk of voters and engages some previous non-voters, it also motivates opponents to turn out and think tactically. 

How that balances out will likely determine future nationwide elections.

For now at least, Reform have taken a big hit. There will be internal recriminations. Farage has alienated many allies/rivals over the years, from Robert Kilroy-Silk to Ben Habib and Rupert Lowe. 

Elon Musk and Tommy Robinson are not fans. Implosion is not impossible. Far-right parties are historically vulnerable to fragmentation. The Tories may eye an opportunity to win back some lost votes.

Senedd Voting System Favours Plaid

Regardless of whether that happens, opponents of Reform demonstrated electoral nous on Thursday, uniting around the party who were best-placed to beat them. 

Voters with that mindset will prefer the PR voting system used in Senedd elections. Reform are unlikely to pick up many second preferences, whereas Plaid (and to some extent Labour, Greens and Lib Dems) must be expected to fare much better. 

A coalition involving those left/liberal/centre parties looks the likely outcome next May.

By the same logic, the Green Party are entitled to feel optimistic about these results.

If Plaid are the principal left alternative to Labour in Wales, and the SNP are in Scotland, the rapid rise of Zack Polanski as an exciting, charismatic leader leaves them poised to hoover up disaffected Labour voters. 

That said, tactical voting is harder in England, and the electorate is much further to the right than Wales. 

It will be much harder to stop Reform or a Reform/Conservative pact there. Nevertheless, again, taking the best-priced 10/11 about Reform winning most seats makes no appeal this far out. 

So much can change, particularly regarding the structure of parties.

Starmer Faces A Grim 2026

Returning to Labour, there is absolutely nothing positive to take. They are facing a challenge like never before in their history. 

No party has ever outflanked them on the left but now there is a different one in Scotland, Wales and England. 

There is no obvious rabbit in the hat to pull out and save them before the May elections.

Those elections could well spell the end for Sir Keir Starmer. He is now a best-priced 11/8 to leave office in 2026 with StarSports, 4/1 to do so in 2027, and 1/2 anytime before the next general election.

Who will gain the most seats in the Senedd next year? Vote now, or let us know in the comments below!