However, Boris Johnson repeated his assertion that a Leave vote would amount to "independence day" for Britain.
The final messages come on the eve of the historic EU referendum, a decision that will shape the direction of the country and its place in the world for decades.
Latest polls though show that Britain is a nation divided.
Polls have consistently shown voters - a record 46.5 million of whom have registered - split down the middle, with the outcome too close to call.
Speaking at a 'Rally to Remain' event in London on Wednesday were Jeremy Corbyn, leader of the Labour party, Sadiq Khan, Mayor of London, Carwyn Jones, the First Minister for Wales and Kezia Dugdale, leader of the Scottish Labour Party.
Each set out their case for voting to Remain ahead of polling day tomorrow.
Corbyn told the gathering, "Tomorrow, if we vote to leave the EU then we will reject cooperation that has brought us closer together.
"Throughout our history, the people of Britain have looked outwards for ways to work with others to improve the lives of our fellow citizens and the world around us. It is this commitment to delivering real change for all which forged the Labour party.
"We believe Britain is better off in the EU not because we don't think Europe needs reform, it clearly does, but because it offers the best cross-border framework that we have to defend living standards, rights and protections for all our people.
"By voting to remain we can protect jobs linked to Europe, defend workers' rights from Tory leaders who want to scrap them and safeguard our NHS from the threat of runaway Tory cuts and privatisation.
"So I urge Labour supporters this Thursday do what's best for our people, vote for jobs, rights at work and our NHS, vote Remain."
At the same rally, Khan, who appeared on a major TV debate on Brexit on Tuesday, said, "We in the Labour party face the fight of our lives between now and polls closing tomorrow night. We are here today to make the strong, positive and Labour case for Britain remaining in the EU.
"As Labour leaders for countries and regions across the UK, we are totally united in our conviction that staying in Europe will be better for the people we represent - better for jobs, rights, security and Labour values.
"So I urge every Labour supporter to get out there in the short time we have left and spend every second and every hour persuading your friends and neighbours to vote for Britain to remain in the EU."
His sentiments were endorsed by Dugdale, who told the rally, "I know what it's like to campaign hard in the final few days of a referendum vote that will determine the future of our country for generations to come.
"A campaign that has divided our nation like never before. Where experts are dismissed and facts are a mere inconvenience.
"This vote will go down to the wire, just as the vote in 2014 did. Polls suggest that as many as 10 per cent of voters remain unsure how to vote.
"Many of them won't finally make up their mind until they are walking into the polling station. What they ultimately decide will make the difference in this referendum."
Meanwhile, Jones declared, "Walking away, going it alone is not in Labour's DNA. And I know it has never been in Wales' best interests either. We are the party of togetherness, we are the party that brings people together - to protect communities from the harsh edges of globalisation and to provide fairness and opportunity for all.
"A future outside the EU would be absolute anathema to that vision. Walking away would make us weak. Walking away would be a betrayal of our working people.
"Walking away would tell inward investors that we are no longer open for business. That would be a disaster for Wales, where our record employment rates are now better than the rest of the UK."
Speaking separately, leading Leave campaigner Boris Johnson, a member of the UK Parliament and former London mayor, described the EU as "a job-destroying engine."
"You can see it all across southern Europe and you can see it alas in this country as well," he said, lambasting Brussels for imposing a "multitude of regulations" on British business.
Johnson said it was the Remain camp that was guilty of drumming up fear, arguing that a Brexit offered "hope."
"If we vote 'Leave,' we can take back our country," he said. "This Thursday can be our country's independence day."
The Leave campaign has received more funding than its opponents, according to the latest figures from Britain's electoral commission.
They showed that the pro-Brexit camp received just under £15.6m in donations, while Remain got £11.9m from 1 February to 9 June.
Meanwhile, European Commission President Jean-Claude Juncker will not step down if Britain votes to leave the EU in the referendum, his spokesperson said.
"The answer is no," spokesman Margaritis Schinas said on Wednesday when asked if, in the light of media reports about Juncker's health, he would resign in the event of a Brexit.