With just two days to polling day, a Survation poll for ITV's Good Morning Britain put the two main parties almost neck-and-neck, with the Tories on 41.5% and Labour on 40.4%.
The dramatic tightening has not been reflected by all pollsters - with some weekend surveys suggesting the Conservatives still enjoy a double-digit lead.
But with polling companies across the board reporting a closing of the gap since Theresa May called the election in April, Mr Johnson will use a campaign speech in the North East to raise the prospects that the Conservatives could lose their Commons majority.
“It makes me shudder to think that we could seriously be about to elect a Corbyn-led coalition that would impose destructive new taxes on businesses, on homes, on gardens - at the very moment when we could be about to go forward with Global Britain,” he will say.
“This is the moment to believe in the huge potential of Brexit Britain. Let's get Brexit done. Let's get Brexit right. Let's believe in Britain. And let's work for the next 48 hours to make sure our negotiations are led by Theresa May and the Conservatives.”
His comments will been seen as an attempt to galvanise Conservative supporters to turn out and vote by raising fears that Mr Corbyn could be on the verge of gaining the keys to Downing Street.
They came as Labour claimed that Conservative plans to scrap the winter fuel payment for better-off pensioners could lead to almost 4,000 additional deaths this winter.
In an interview with The Daily Telegraph, Mrs May again sought to make security a key issue in the wake of the London and Manchester terror attacks - contrasting her record with that of the Labour leader.
“There is a very sharp contrast for people on Thursday,” she said.
“I've been willing to introduce new powers for the police, I support shoot to kill, Jeremy Corbyn has been very clear that he has opposed every piece of anti-terrorism legislation, he doesn't support shoot to kill.”
The Prime Minister, who has faced criticism over police cuts during her time as home secretary, again indicated that she would consider new powers to block access to extremist websites if the internet companies failed to deal with online radicalisation.
“I think it is important we do get together internationally and look at the possibility of regulating cyberspace because what has developed as generally a huge benefit for people, is being misused because it's being used as a tool in helping to put together attacks,” she said.
While Mrs May said she believed women should be allowed to wear burkas, she emphasised the importance of women from Muslim communities being able to speak English so they could participate fully in UK society.
“I've always said that a woman should be able to choose how she dresses,” she said.
“What I think is important, though, is that women are able to participate fully in society and aren't treated as second-class citizens and, of course, one of the things that we do see is women who are living here but don't speak English.”
Labour, meanwhile, has released an analysis suggesting the Conservative's plans to means-test winter fuel allowance for pensioners could lead to 3,850 additional deaths over the winter.
Shadow Chancellor John McDonnell said: “Re-electing the Tories will represent the single biggest attack on pensioners in a generation in our country.”
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