Starmer warns of 'back-room' stitch-up ahead of Senedd poll

In a speech to the Welsh Labour conference, the Prime Minister is set to say that a coalition of those parties would be a “return to the chaos and division of the last decade” and risk rolling back the progress his party is starting to make.

“Whether that's with Reform, or with Plaid’s determination to cut Wales off from the rest of the country - with no plan to put Wales back together,” he is expected to say.

Reform UK is eyeing an opportunity to end Labour's 26 years of domination in the Welsh Parliament at the Senedd elections in May next year.

Labour performed poorly in this year’s local elections in England, which saw Nigel Farage’s party win a swath of council seats.