David Cameron and Jeremy Corbyn have told rallies in Bristol and London that a Remain vote in Thursday’s poll will mean the UK is safer and better off, BBC reports.
But Boris Johnson said a vote to leave would show people “believe in our country” and Nigel Farage urged people to act “with their heart and soul”.
More than 46 million people are eligible to vote in the referendum.
The UK public are being asked to choose whether the UK should stay in the European Union or leave in the first vote on the country’s membership of the bloc for more than 40 years.
The four-month campaign is reaching a climax with last-minute appeals to undecided voters from both sides.
David Cameron, who appeared alongside ex-PM Sir John Major and former Labour leader Harriet Harman in Bristol, said that Thursday decision will be irreversible and there will no coming back if the UK votes to leave.
“You can’t jump out the aeroplane and then clamber back through the cockpit hatch,” he told BBC Radio 4’s Today.
Leaving the EU would be a “massive problem” for the UK, he said, doing “untold damage” to economic growth, jobs and family finances and hindering the opportunities and life chances of future generations.
“If I had to sum up this entire campaign in a word, it would be that word ‘together’. I think together we are better able to face the challenges from terrorism and climate change, we are better able to grow our economies, better able to drive good trade deals… and I want us to get the good deals so we give better chances to everyone in our country.”
Mr Cameron said he “did not believe there were any risks from staying” in the EU, saying the eurozone was beginning to recover economically and this would have an effect on levels of migration into the UK after what he said was an “abnormal period”.
He also said he would lobby for further changes to free movement rules in the light of European Court rulings if the UK votes to remain and said the process of EU reform will “continue on Friday”, insisting that reducing net migration was “not an unrealistic ambition”.
However, European Commission President Jean-Claude Juncker, appeared to reject that option as he told reporters in Brussels “out is out”, suggesting that if there was a vote to leave “there will be no kind of renegotiation”, saying David Cameron “got the maximum he could receive” after months of talks which ended in February.
As party leaders past and present take the stump in the final hours, Sir John Major characterised Leave supporters as “gravediggers of our prosperity” and said Brexit may result in a “broken Britain with less importance and less influence in the world”.
But Boris Johnson and other Leave campaigners said only a vote to leave the EU could give the UK the freedom it needs to set its own course, rejecting the economic forecasts suggesting the country would face a downturn following Brexit.
Speaking in Billingsgate fish market ahead of embarking on a whirlwind tour of England, the former mayor of London urged people to “believe in our country” and seize the moment.
“This is a crucial time, lots of people will be making up their minds, and I hope very much they will believe in our country, believe in what we can do,” he said.
“It’s time to have a totally new relationship with our friends and partners across the Channel. 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.”