LONDON — Londoners responding to a knock on their front doors in recent days may have been surprised to see a familiar face grinning back at them: Hugh Grant, one of the country’s most recognizable actors, who made his mark as the floppy-haired, bumbling leading man in romantic comedies.

But Mr. Grant, who famously played a prime minister going door to door in “Love Actually,” was not looking for a lost love this time. He was looking for votes.

Celebrities have long waded into the political arena, throwing the weight of their public personas behind candidates and causes. But Mr. Grant has become one of the most vocal and active ahead of Britain’s general election on Dec. 12, pounding the pavement with candidates who differ ideologically but agree that Britain should remain in the European Union.

He has campaigned with candidates for Parliament in at least four different London-area constituencies, and he has been spotted on the city’s Underground trains, headed to and from political events.