MPs in warning to Starmer after Labour wipeout in Welsh election

The loss is a blow to Reform, especially after Nigel Farage travelled to the area more than once.

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But Powell said the race had taught the party valuable lessons before next May: "A big part of what we were trying to do here is to master our campaigning. We've trained so many people up on our systems. We're now a grassroots campaigning party."

While the Labour collapse was widely expected, it has brought practical difficulties - it now holds just 29 of the 60 Senedd seats, making it harder to pass its budget - plus a more existential worry that the party has no answers to the challenge faced by Reform and, increasingly, its rival parties on the left.

Many Labour MPs fear that even if similar levels of tactical voting can hold off Reform in some areas, the beneficiaries could often be Plaid in Wales, the SNP in Scotland and the Greens or Lib Dems in parts of England.

"Our strategy is based on the idea we can unify progressive voters around a 'stop Reform' campaign," one MP said. "That works so long as you remain the most viable progressive party. But if people start to think that it's maybe another party, then suddenly that tactical voting starts to work against Labour and you get punished really badly."