LONDON -- Britain's political candidates embarked Sunday on a final push ahead of this week's general election, making last-ditch appeals to shore up support and persuade their backers to go to the polls.

All 650 seats in the House of Commons are up for grabs Thursday when voters will pass judgement on a divisive election that will determine Britain's future with European Union.

Although opinion polls have placed Conservative Prime Minister Boris Johnson in the lead in Thursday's general election, analysts suggest the gap is not wide enough to guarantee a majority in Parliament. Johnson urged supporters at a London rally on Sunday to learn from the 2017 election, which saw former Conservative Prime Minister Theresa May fritter away a decisive lead in the polls and end up with a divided Parliament.

"We're now in the final furlong of this race, and that is when of course the horses can still change places," Johnson said before urging the group to "drive for the line."

"We're going to get there, but only if we work really hard," he said.

Johnson and members of his Cabinet also hit the phones in a bid to gain support, making calls from the Conservative Party headquarters in central London. In one comical moment, Johnson offered his name to one potential voter, but felt the need to add: "I'm the prime minister."

Johnson's cautious message comes in part because Britain's traditional political alliances don't necessarily apply in this election. British voters' 2016 decision to leave the EU has sparked a major overhaul in British politics, and many voters will make their choice based on a candidate's position on Brexit alone, rather than on past political ties.

The Conservatives are also worried that people who voted to leave the EU won't turn out to vote because they are fed up with politicians' failure to carry out the 2016 referendum decision, said Matthew Goodwin, a visiting senior fellow at the Chatham House think-tank .

"One thing to keep your eyes on, the Conservatives are very aware that a lot of their leave voters have gone missing," Goodwin said. "They've gone back into apathy. They're not planning to turn out. One the of the big things they are trying to do with their campaign is find missing leavers"

The main opposition Labour Party has also been moving to shore up votes that it could have counted on in years past. Party leader Jeremy Corbyn campaigned Sunday in Wales -- a part of the U.K. that has been a Labour stronghold for decades. He also urged supporters to take nothing for granted in this vote.

"When you are working, knocking on doors in the rain ... over the next few days, remember what you're doing it for," he said as people cheered. "You're doing it for the next generation. You're doing it to change the course of political history in Britain. Go flat out!"

Johnson pushed to hold the December vote, which is taking place more than two years early, in hopes of winning a majority and breaking Britain's political impasse over Brexit. He has pledged 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 Brexit deadline.

Labour says it will negotiate a new Brexit deal, then give voters a choice between leaving on those terms and remaining in the bloc. Labour's eye-catching domestic agenda has included promises to nationalize key industries and utilities and give free internet access to all.

But the Labour campaign has been beset by allegations that Corbyn -- a long-time champion of the Palestinians -- has failed to stamp out anti-Jewish prejudice in the party. In another blow, the Mail on Sunday quoted Rabbi Marvin Hier, the head of the Nazi-hunting group, the Simon Wiesenthal Center, as saying that "no one has done more to mainstream anti-Semitism" than Corbyn's Labour Party.

Labour's John McDonnell acknowledged that the issue could hurt the party in the upcoming vote.

"I apologise to the Jewish community for the suffering we've inflicted on them, I say to them we're doing everything possible," he told the BBC. "We want to learn more lessons and we want to be the shining example of anti-racism that the Labour Party should be."

Labour is also being challenged on how it obtained government documents on exploratory talks on a Brexit trade deal with the United States. The documents had appeared on the social media platform Reddit for weeks before Labour brought the documents into the election debate just days ago.

Johnson called for an investigation Saturday "to get to the bottom" of the release after Reddit concluded that people from Russia leaked the confidential British government documents.

Reddit said in a statement late Friday that it has banned 61 accounts suspected of violating policies against vote manipulation. It said the suspect accounts shared the same pattern of activity as a Russian interference operation dubbed "Secondary Infektion" that was uncovered earlier this year.

But Johnson has troubles of his own on the question of whether Russia is meddling in the vote. Critics have been challenging the British government's failure to release a Parliament intelligence committee report on previous Russian interference in the country's politics. They say it should have been made public before Thursday's vote.