This result of course was driven in no small part by significant defections to both Plaid Cymru and Reform from disillusioned former Labour voters. This was the overwhelming sense we got from our focus group in Caerphilly, with voters defecting to left and right describing a weariness with a double-incumbency of Labour in Wales and Westminster. More broadly, there was a sense that Labour is losing its connection to the Welsh Valleys.
 
“I’ve been a lifelong labour fan. But I never thought I'd see a labour government take money away from pensioners (...) I've never seen politics so adrift. I think they've totally lost touch with the people and I think politics is broken, which is leading to Britain and Wales being broken.” 
Martin, call centre manager, Labour to Plaid Cymru switcher
 
“I think you saw how bad things were getting after 14 years of the Tories and voted Labour and thought, oh here we go, finally things are going to turn around and I think they've just accelerated what the Tories were doing and things are getting even worse at a quicker pace. There's been too many scandals in a year or just over a year”
Derek, transport engineer, Labour - Reform switcher
 
“You do see reform absolutely everywhere, but it's kind of like we have been as Wales or South Wales have been quite strong at voting labour for many, many years And it's kind of like that's all we know (...) So I think people have got kind of a bit fed up of what we know and want to change, but really don't really know what the change is.”
Fiona, maternity leave, Labour - Reform switcher
 
With the highest turnout the Senedd constituency has ever had - and higher than the national turnout at any Senedd Election, the by-election shows that Reform is mobilising voters en masse - both those who are turning up to vote for Reform, and those who are turning up to oppose it.
 
Tactical voting was essential to the size of Plaid’s victory, once it became apparent they were the stop Reform party they gained as a result and that undoubtedly magnified their majority. This reflected what we heard in our conversations with voters in Caerphilly. While Reform is rapidly gaining popularity across Wales, we hear from some Welsh voters who remain averse to the party, sometimes put off by their lack of a Welsh leader, or a broader sense that Reform is a primarily English party that does not care about Wales. Meanwhile, Plaid has broadened their appeal, and proven that they can win over working class voters in communities that had previously been loyal to Labour.
 
This result shows that Reform has further work to do to de-risk the party in Wales. While the proportional voting system means that tactical voting will likely be less significant in next year’s Senedd election, if Reform hopes to top the poll in Wales in the next Westminster election (as our September MRP suggests is possible), they’ll need to insulate themselves from the risk that progressive voters tactically unite to keep them out by building out beyond their core base of support. 
 
Similarly, with the upcoming budget and throughout the next few years in government, Labour may need to make a deeper offer to their progressive voters - in order to show they do represent real change, and prevent their left flank drifting to the Liberal Democrats and Greens, and enabling themselves becoming the beneficiaries of tactical voting. 
 
“If Reform get in, it would be a catastrophic moment for me. I've always thought about Plaid. If I didn't vote Labour then I'd vote Plaid. In a way a national Assembly, having a bit of a national party sort of like Scotland, it sort of makes sense to me because feeling like they're going to look after you a bit more as a bit of a connection I suppose.”
 Gareth, civil servant, Labour - Plaid Cymru switcher
 
Is labour becoming the party of the status quo?
 
In our Westminster voting intention this week, we noticed two interesting things.
 
The first was that the Green Party has hit double digits, reaching 10 percent for the first time since April. Many pollsters have recorded a similar bounce for the Greens, suggesting that Zack Polanski's energetic campaigning may be beginning to cut through.
 
The other thing we noticed was an interesting pattern in the financial wellbeing of different voter groups.
 
Labour leads Reform by 11 points among those who say they are “very comfortable financially”. But they trail Reform by 16 points among those who say they often struggle to make ends meet. In fact, with 16 per cent of the vote, the Green Party are very close to overtaking Lab for 2nd place with those who struggle to make ends meet.
 
The two main parties’ vote shares peak among Britons who are comfortable, and drop sharply with age. Whereas insurgent anti-establishment parties perform much better with Britons who feel financially insecure.