Caerphilly By-Election Odds: Plaid Cymru to stop Reform UK in Welsh Senedd Vote?

Thursday sees a by-election in the Senedd as the constituents of Caerphilly go to the ballot box to send a candidate to represent them for a short six-month stint. 

Labour are defending a 5,078 majority but the betting suggests they are going to come a distant third. This should be a straight Reform UK vs Plaid Cymru battle but who will come out on top? We have a look as we delve into the Caerphilly By-Election Odds here on Betfred Insights...

*You can bet on and check out the very latest Caerphilly By-Election Odds over on betfred.com

Sir Keir Starmer needs some good news. His approval rating is still in the negative according to pollster YouGov and when I say negative, it’s under water. Just 24% of respondents have a favourable view of the Prime Minister compared to 68% of people who see him in a positive light. 

His positioning of the Labour Party can fairly be described as right of centre as he continues to try and woo Reform UK voters. It is exactly the tactic the Conservative Party have used unsuccessfully in recent years and the Red Rose seems to be following the same path. It is just poor politics and his future as leader seems to be up for discussion, with Andy Burnham the name on the lips of many.

So what better than a Senedd by-election in a seat that has only ever been represented by a member of the Labour Party to restore some good feelings to the beleaguered man residing in Number 10 Downing Street?

Well the problem is, Labour aren’t going to win. They are not even going to finish in the top two if you consider the odds to be a fair representation of the likelihood of emerging victorious. This is a straight battle between Reform UK - who are looking to win an election for the Senedd for the first time - and Plaid Cymru - who are looking to finally get over the hump having finished second in every election in this constituency for the Welsh Assembly since devolution back in 1999.

With Labour’s numbers looking so poor in Wales, their chances of holding the seat seem genuinely remote. Betfred have them at 33/1 to win and that isn’t big enough to entice me. 

In 2025, Labour, Reform UK and Plaid Cymru have all led various Welsh polls, which on the face of it does seem to indicate that they are at least in the mix. The truth is though that with Plaid having so much strength in the seat, they are a very natural home for the disgruntled Labour voter in this by-election. They could easily take 10-15% of their vote and that would be enough to overturn the majority. 

The wildcard is Reform UK. If everyone who says they will vote for them actually turns up at the ballot box on Thursday, then they very much should be favourites. We all remember the 2014 European and Local elections in the UK when UKIP just swept all before them on a low turnout as their supporters were extremely motivated. The question I have is whether they’ll be that keen for a Welsh by-election that will send a candidate to the Senedd for a short six-month term?

Both Reform UK and Plaid Cymru have thrown the kitchen sink at this election. For both, it would be a huge win. If Nigel Farage’s party get the victory, they can say they’ve got a foothold in Wales and if Rhun ap Iorwerth’s party get the win, then they can claim to be the best non-right wing choice in a seat they’ve traditionally been strong in for elections both to the Senedd and Westminster going forward.

Reform UK are 4/11 as of the time of writing with Plaid Cymru trading at 2/1. I would much prefer to be on the bigger price as I’m not convinced that the motivation is there for Nigel Farage’s supporters to send a message. This is a true toss-up by-election that is likely to be won/lost by under 500 votes, so back the party with the bigger price.