LEAVING the EU is an 'irreversible decision' that would do lasting damage to the UK economy, David Cameron has warned.

Speaking as the referendum campaign entered its final three days, the Prime Minister said it would be a 'tragedy' if Britain quit the EU on the basis Leave campaign claims he said were 'simply untrue'.

Mr Cameron repeated his stark warnings about the impact of Brexit on the economy during a special edition special edition of the BBC's Question Time programme.

He warned it could take the economy 'back to square one' after efforts to pull out of the recession caused by the banking crash eight years ago and lead to higher borrowing, tax rises or spending cuts.

Contemplating a possible Brexit vote on Thursday, he added: "I do believe it is irreversible.

"If we vote to leave I don't think there is any prospect of rejoining.

"This is a final decision. We can't jump out of the aeroplane and try to scramble back into cockpit."

In an often passionate performance before an audience in Milton Keynes, he also compared Britain's ongoing partnership with EU countries to Churchill's decision to go to war with Hitler's Germany.

The Prime Minister vented his anger at the Leave camp's claims that Turkey was about to join the EU, that a European army was being created, and that Britain sent £350million per week to Brussels.

As campaigning resumes today after a pause following the brutal killing of MP Jo Cox, the Remain campaign will underline its focus on the economy when it unveils a joint statement by 10 Nobel Prize-winning economists saying the UK "would be better off economically inside the EU".

The group, including Professor Sir James Mirrlees, a member of Nicola Sturgeon's Council of Economic Advisers, say Brexit would "create major uncertainty" over trade that would "would persist for many years".

In his Question Time appearance, the Prime Minister repeated a series of messages he set out earlier in an article in a Sunday newspaper.

Writing in the Sunday Telegraph, he said there would be "no turning back" if Britain voted to leave on Thursday and warned it could lead to "debilitating" economic uncertainty for up to a decade.

In a similar warning about the economic impact of Brexit, George Osborne said leaving the EU would be a "one-way door to a much more uncertain world".

He said he thought the hit to the economy if Britain votes to leave on Thursday might be worse than the 5 per cent slump officially forecast.

The Leave campaign hit back, saying the Prime Minister had questions to answer about his support for Turkey's accession to the EU.

Bookmaker William Hill made Remain the 3/10 favourite in Thursday's referendum, with Leave an outside chance at 5/2.

The odds tightened in favour of Remain after a Survation poll, conducted by phone on Friday and Saturday, as nation mourned slain MP Jo Cox, showed Remain on 45 per cent and Leave on 42 per cent.

Ukip leader Nigel Farage said the MP's tragic killing had stemmed the momentum of the Leave campaign.

Following pleas for the debate to become more restrained in the wake of Ms Cox's killing, Mr Farage came under renewed attack over a highly emotive poster he unveiled last week claiming Britain was at "breaking point" over immigration.

Nicola Sturgeon, who branded it "vile and racist," joined chorus of voices denouncing the Leave camp's tactics.

In other developments, the veteran financier Sir Angus Grossart called on Brussels to deliver a "vow"-style commitment to reform in final few days before polling. He said he had not yet decided how to vote.

Another business figure, CBI president Paul Drechsler said the prospect of Brexit was a major cause for concern for firms in Scotland.

Speaking before addressing CBI members in Edinburgh, he told The Herald a vote to leave the EU could cast into doubt a range of things that businesses rely on.

Ms Sturgeon made a candid plea to independence supporters, urging them not to back Brexit in the hope of triggering a second independence referendum.