LONDON — Britain’s center-left Labour Party has defeated the center-right Conservative Party in a historic landslide and will return to power after 14 years, according to the exit poll. Labour’s Keir Stamer, a former lefty lawyer-turned-ruthless centrist, will become the nation’s next prime minister, relegating incumbent Rishi Sunak’s Conservatives to official-opposition status. Starmer said voters across the country had sent a message that it was time to end “the politics of performance” and “return to politics as public service.”