Why is a Welsh by-election so important for the UK?

This week’s by-election in Caerphilly may end up being the only one in the history of the Wales Senedd.

- JOHN RENTOUL

Caused by the death of Labour member Hefin David, it is the first since the Welsh assembly changed its name to the Senedd five years ago; next year, a new Senedd will be elected by a new proportional system that abolishes by-elections. Under the closed list system, any vacancy will be filled by the next person on that party's list.

The contest has also become a significant pointer to the changing shape of Welsh politics, where the rise of Nigel Farage's Reform party could have implications for the next general election in the whole of Britain.

Why is Wales a Reform target?

Nigel Farage launched Reform's manifesto - sorry, its “Contract” - in Merthyr Tydfil in the general election campaign last year, after he made the shock decision to return to the leadership of the party. Even then, Farage could read the opinion polls and judge that Wales was promising territory for Reform.

Since the general election, Reform has gained ground in Wales, as has Plaid Cymru, the Welsh nationalist party. The two parties are vying for the lead in the opinion polls, while Labour has dropped below 20 per cent support and the Conservatives to below 10 per cent.