LONDON — Campaigners on both sides of the crucial vote over whether Britain should remain in the European Union crisscrossed the country Wednesday, their last day to win support from the undecided.

Prime Minister David Cameron outlined his vision for a future with Britain retaining its place in the 28-nation bloc, bristling at the notion that the country would be headed in the wrong direction if it stayed in. He flatly rejected the charge that the institution is moribund.

“We are not shackled to a corpse,” Cameron told the BBC. “You can see the European economy’s recovery. It’s the largest single market in the world.”

The most notable figure in the “leave” campaign, former London Mayor Boris Johnson, kicked off a whirlwind tour of England as he pushed for a British exit — or Brexit. Touring the Billingsgate Fish Market, Johnson mugged for the cameras with fish in hand — a not-so-subtle reminder that this is an island nation — and one very proud of its independence and self-assurance.

“It’s time to have a totally new relationship with our friends and partners across the Channel,” Johnson said. “It’s time to speak up for democracy, and hundreds of millions of people around Europe agree with us. It’s time to break away from the failing and dysfunctional EU system.”

Voters go to the polls Thursday after a campaign that has been unusually heated, even by the lively standards of British politics.

Nigel Farage, a “leave” campaigner and leader of the U.K. Independence Party, resisted fresh calls to apologize for a poster showing hundreds of migrants making their way across Europe along with the words “Breaking Point.”

The poster, labeled racist and misleading by opponents, was unveiled hours before Labour lawmaker Jo Cox was killed in a knife and gun attack outside a library in her Yorkshire constituency last week.