Why has UK Reform’s Nigel Farage resigned as MP? What happens next?

Nigel Farage has resigned as an MP amid allegations of undeclared donations, triggering a by-election in his Clacton constituency where he plans to stand again. Other major parties say they will not field candidates, allowing Farage to frame the vote as a contest between himself and the political establishment. The move comes as his Reform UK party has surged in opinion polls, reflecting growing anti-immigration sentiment across the country.