The candidate for Reform U.K., the right-wing party of British lawmaker and ally of President Donald Trump, Nigel Farage, won a parliamentary by-election by six votes, taking the seat from the governing Labour Party in a stunning political upset.

The upstart Reform UK party has emerged as a serious contender in British politics. The anti-immigrant populist movement has overtaken the main Conservative opposition to jostle with the ruling Labour Party for the lead in opinion polls,