Before a Debate, the U.K. Election Campaign Just Got Messier

Prime Minister Rishi Sunak and Keir Starmer, the leader of the opposition Labour Party, will square off on Tuesday evening in their first debate of Britain’s general election. But it is a third man, Nigel Farage, who has seized the spotlight in a race defined, until now, by a fading incumbent and a rising opponent.

Mr. Farage, a gleeful insurgent who has long roamed the right-wing fringes of British politics, said he would run as a candidate for Reform U.K., a party he co-founded. That has shaken up the race and threatens to siphon off votes from Mr. Sunak’s Conservative Party, given Reform U.K.’s strident anti-immigration message.

Mr. Farage’s entry into the race is not by itself transformative. He has run for a seat in the British Parliament seven times — and lost every time. But his return could breathe momentum into other Reform U.K. candidates, throwing yet another hurdle into Mr. Sunak’s path between now and the vote on July 4.

The prime minister is struggling to avert a landslide defeat to Labour, which has held a double-digit polling lead over the Conservatives for more than a year. His debate with Mr. Starmer, though early in the campaign, already looms as a make-or-break chance to change a fast-congealing narrative.

“The election is over; it is done; Labour have won the election,” Mr. Farage said in declaring his candidacy in a surprise announcement on Monday. Describing it as “the dullest, most boring general election campaign we have ever seen in our lives,” Mr. Farage, 60, said the race needed “gingering up,” and offered himself as the tonic.

Mr. Sunak called the election on May 22, several months earlier than expected, in part to exploit a few glimmers of good economic news. He has moved aggressively to appeal to voters who might be attracted to the hard-right Reform U.K, proposing a national service requirement for 18-year-olds and floating a new law that would bar transgender women from women’s restrooms and female-only prisons.