British Conservative Party lawmaker Boris Johnson leaves his home in London, Tuesday, June 11, 2019. Britain’s Conservative Party is holding an election to replace Prime Minister Theresa May, who resigned last week after failing to lead Britain out of the European Union on schedule. Former Foreign Minister Boris Johnson is currently the bookies favorite to replace May. (AP Photo/Frank Augstein)

LONDON (AP) — British Prime Minister Boris Johnson and opposition leaders were pushing for the finish line in Britain’s election campaign Monday, dashing through multiple constituencies to drum up support in the final 72 hours before polling day.

Johnson was touring Labour-held seats across England that his Conservatives have to win if they are to secure a majority in Thursday’s election. Labour Party leader Jeremy Corbyn was in southwest and central England, where his left-of-center party is trying to hang on to key constituencies.

Opinion polls give Johnson’s Conservatives a lead, but as many as one in five voters remain undecided. This election is especially unpredictable because the question of Brexit cuts across traditional party loyalties.

Underscoring the significance of those shifting allegiances, Johnson’s first stop was in the eastern port town of Grimsby targeting Labour voters who also backed leaving the European Union in the U.K.’s 2016 referendum.

Wearing a white jacket, hat and rubber boots, Johnson lugged a crate of fish across the floor of a fish market in the town that has been in Labour Party hands for 74 years — and said he was “taking nothing for granted” in the final days of campaigning.

The Conservatives had a minority government before the election, and Johnson pushed for the vote, which is taking place more than two years early, in hopes of winning a majority of the 650 House of Commons seats and breaking Britain’s political impasse over Brexit. He says that if the Conservatives win a majority, he will get Parliament to ratify his Brexit divorce deal and take the U.K. out of the EU by the current Jan. 31 deadline.

Labour is promising to renegotiate the divorce deal, then give voters the choice in a referendum of leaving the EU on those terms or remaining in the bloc.

Speaking in London, the party’s finance spokesman, John McDonnell, outlined what a Labour government would do in its first 100 days if elected — including making good on election pledges to nationalize public utilities and launch a “green industrial revolution” to tackle climate change — as well as hammering out a new Brexit deal to be put to a second referendum.

“Despite all his promises, it is clear to all now that far from getting Brexit done, under Johnson Brexit won’t be done for years or we risk a catastrophic no deal,” McDonnell said.