Caerphilly result is blow to Labour and Reform – and shows parties who cannot adapt will be crushed

Plaid Cymru’s byelection victory signals a seismic shift in Welsh politics that will rattle Westminster

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If anyone inside No 10 allowed themselves a sigh of relief at Reform UK’s advance being stymied in the Caerphilly byelection, they would then have heard the warning from Lindsay Whittle, Plaid Cymru’s winning candidate: “You are on your way out after 100-plus years.”

Labour in Wales might or might not be “a dying beast”, as Whittle argued, but this one-off Senedd race illustrated how it was on course to lose its grip on Welsh politics in May, with potentially wider implications for Keir Starmer and his party.