LONDON, Aug. 16 -- Nine thousand, four hundred and fifty-five people in Clacton voted last Thursday for a man whose campaign helmet is a rubbish bin and whose platform included capping the price of croissants. That number does not represent a political uprising. It represents something Nigel Farage may find harder to explain away than the margin of his victory.

Farage, the leader of the far-right Reform UK party, reclaimed his parliamentary seat in the Clacton by-election with 22,239 votes, defeating 33 other candidates in a contest he himself had triggered. He had resigned the seat in July amid an investigation into an allegedly unreported £5 million donation to his party from a cryptocurrency billionaire, a resignation he framed a...