The danger for Labour in the election no one wanted

Eluned Morgan's party could have a harder task passing a budget if it fails to regain Caerphilly

It goes without saying that this is a by-election that, for obvious reasons, no one in Welsh politics wanted.

That does not mean that there will not be a fight to win the seat.

With the caveats that you should not read too much into a by-election and that it will use a different voting system to next year's Senedd election, it could nonetheless give us a pointer as to what might happen in May 2026.

There's also short term danger for Labour: lose and it would end up with 29 of the 60 Senedd seats which could make things like passing a budget trickier.

The fight in Caerphilly has already begun.

Voters will see at least one familiar name on the ballot paper after Plaid Cymru named Lindsay Whittle as its candidate, whose last attempt - of multiple attempts - to win the seat was at last year's general election.

Labour hope to name its candidate on the weekend, with the Conservatives shortly to start its selection process.

Some in Labour privately acknowledge it will struggle to hold on.

Others in the party see the potential for a three-way fight against Reform UK and Plaid Cymru.

That in itself shows how much things have changed since the last Senedd election in 2021.

Hefin David won with 46% of the vote with a majority of more than 5,000 over Plaid.

Reform managed just 495 votes; 2% of the total.

Albeit under slightly different boundaries Labour also won at last year's general election, more than 6,000 votes clear of Plaid with Reform not far behind.

But Labour's vote share fell by nearly 6%, with Plaid's and Reform's growing by 6.5% and 8.6% respectively.

That said, there is a determination in Labour to win, even if polling suggests it will struggle.

Hefin David died suddenly last month.

Both Reform and Plaid Cymru fancy their chances.

Those polls suggest that either Nigel Farage's or Rhun ap Iorwerth's party will win most seats at next year's Senedd election, with Labour in third place.

If Labour were to lose in Caerphilly then it could cause the party problems before next year's poll.

Finance Minister Mark Drakeford has already announced he will present a "neutral" budget for next year, which will repeat this year's spending plans – with the addition of an unallocated £400m for the next government to spend as it sees fit.

This year's plans were passed after a deal with the sole Lib Dem MS Jane Dodds, but if Labour does drop to 29 seats it would need at least one extra MS on board.

Both the Welsh Conservatives and Plaid Cymru voted against the budget.

Budget conversations – as they always are at this time of year – are underway within Labour, with an eye on the fact that passing it could end up being trickier than planned.

If it starts to get complicated, how much of a distraction might that be when ministers might prefer to be concentrating their energy on campaigning for the Senedd election?

Opposition parties in the Senedd are already pondering what sort of concessions Drakeford might offer and are acutely aware of the potential problems a Labour defeat in Caerphilly could cause.

They would also need to bear in mind whether there would be any political risk in 'propping up' the Welsh Labour government so close to a Senedd election were they to be tempted by any offer of a deal.

One final thought is the length of the by-election campaign. It is quite long.

That gives parties and candidates time to get themselves into the spotlight, but also gives more time for something to go wrong.