Caerphilly By-Election Betting Odds: Outsiders Are Value In Unpredictable Race

For probably the first time ever, a by-election for the Welsh Senedd takes centre stage in UK politics this week, and that is certainly the case when it comes to action on politics betting sites.

Why? Three reasons. First, it is a genuinely competitive, unpredictable contest involving several known unknowns. 

Second, it will offer strong clues towards next May's nationwide elections to the Senedd. 

Third, it seems certain to demonstrate the dramatic transformation ongoing in Welsh politics and to a large extent, the UK in general.

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Catastrophe For Labour Widely Expected

The Caerphilly by-election was called following the death of MS Hefin David, the latest in a long line of Labour representatives in a seat which was about as Labour a stronghold as they come. 

He won the seat by an 18% margin from Plaid Cymru last time. As for the Westminster constituency, they beat the Conservatives by a 17% margin in 2019, on these boundaries, on the same day that Jeremy Corbyn suffered a historic defeat across the UK.

Put simply, Labour have never faced a strong challenge. Now, they are widely expected to finish third, at best. The battle lines of Welsh politics are being redrawn as the old order collapses. 

The existential crisis facing the Conservative Party and mass drift of their voters to Reform is well documented. But for Labour, this expected loss is a historic low. A total catastrophe and dire signal of what is to come next May and perhaps beyond.

Can Reform Justify Favouritism And Build Momentum?

For Reform, this is a golden opportunity to state their credentials as favourites to win the Senedd in May, and most seats at the next UK General Election. 

They are odds-on for both - at 4/5 with Bet365 for the former, and 16/19 with Unibet for the latter. 

For Caerphilly, the odds, pretty much across the board on betting sites, are 2/5 for Reform, compared to a best-priced 9/5 for Plaid Cymru.

It seems clear that this will mirror the fight for most seats in the Senedd next May. Whilst ex-Conservative voters are transferring en masse to Reform, a large chunk (though not all by any means) of Labour's base are switching to PC.

Caerphilly By-Election Betting Odds:

Only Limited Polling Evidence Available

There has been only one poll of the constituency, for Survation, which recorded Reform ahead by 42-38. 

Their numbers show 70% of former Tory voters switching to Reform, with Labour defectors splitting slightly more to PC than Reform.

Beware reading too much into this poll. There were only 501 respondents and races like this are very hard to poll, because turnout is so unpredictable and differential. 

There have only been four previous by-elections for the Senedd, for which turnout ranged between 22-50%. The poll discarded undecideds and respondents who refused to answer. 

Whilst that methodology is fair, in this particular scenario it raises doubts. 

Given the flux, there were bound to be large numbers of undecideds earlier in the campaign, and there is a strong argument that Reform voters are less likely to participate in polls or admit their preference.

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The Case For Reform

Several points strengthen the case to back Reform. They overperformed at last year's council elections across a range of seats, suggesting their support may be hard to poll. 

They thrived among Labour's working class base in the Runcorn and Helsby by-election and definitely have potential to grow among this type of demographic. 

Their voter coalition is older than PC, and therefore likelier to turn out in smaller elections such as this.

The demographic indicators and MRP projections at Electoral Calculus have been a tremendous help in predicting constituencies lateky, and they currently project a general election victory for Reform in the Westminster constituency, with estimates of 32/23/23 compared to PC and Labour.

The Counter-Argument For Plaid

Those arguments justify odds-on favouritism, but there is a decent counter-argument too. 

The last two YouGov polls for the Welsh Senedd put Plaid on 30% - higher than Reform have ever recorded in any poll - and they were within 2% with both More In Common and Findoutnow. The last two generally produce strong UK-wide polls for Reform.

This doesn't alter the broad perception in that, while Reform are strong right now, they have a ceiling and maybe are at or even past their peak having hoovered up anti-government sentiment due to blanket publicity. 

Plaid, though, appear to still be on the up. There is definitely potential for a tactical, anti-Reform coalition in the long-term to grow, as the framing for each election becomes clearer. 

Plaid Go Local

Reform’s campaign hasn't exactly been perfect, with former Welsh leader Nathan Gill convicted, having pleaded guilty to taking money to push Russian propaganda. 

Their ground game probably isn't as strong as Plaid, who will have been embedded here for a long time, as the clear opposition. Their campaign has been locally focused, on library cuts for example.

Based on the Electoral Calculus numbers, and the fact Labour are being widely reported as in freefall in the constituency, Plaid could plausibly pull off the upset. 

Turnout will be critical, as ever in by-elections. It will probably top 40%, given the interest and competitive race. 

That said, while Reform should get to 40% as the polls imply, they will have little room to grow. 

However, Plaid, who scored 28% in the last Senedd election, and are at 38% in that one Caerphilly poll, can also get to 40% and beyond. They represent slight value at 9/5 in what is expected to be a very close race.