THE debate over Europe risks being “dragged into the intellectual gutter” by increasingly bitter Tory infighting, Shadow Chancellor John McDonnell warned yesterday.

On a day in which voices of the left dominated the EU debate, McDonnell warned the right were “disfiguring political discourse” and people were tired of the “ranting hysteria”.

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Urging progressives to “step in and save the debate” from degenerating into more name-calling and acrimony, he said: “Our country and our people deserve better than this.”

Addressing a meeting in London called Another Europe is Possible, he said the Tories were distorting the EU debate with "the gang warfare of the Eton playground and the battle over the Tory leadership succession".

He said: "[Boris] Johnson's comparisons of the EU to the Third Reich and (David) Cameron's claims of impending World War Three, they just beggar belief. We cannot let the right drag this debate into the intellectual gutter."

McDonnell said the EU offered a way to tackle transnational problems such as climate change, tax dodging and the refugee crisis.

“We have the opportunity [for] a debate on a democratic Europe. A Europe that is not just possible but is urgently and vitally needed - where we can say yes, we are proud of being British, but we are also proud of the European future we have created."

At the same event, former Greek finance minister Yanis Varoufakis, although a ferocious critic of EU austerity cuts in Greece, urged the UK to vote Remain on June 23.

"It is impossible for the EU to become democratised without democratic Britain participating in the process," he said.

"Voting to leave the EU will only benefit a national oligarchy and class which is particularly keen on ruling over the British people completely and utterly undemocratically."

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He said public services in parts of the UK were under strain, but not because of immigration, as the Out camp claimed.

“The reason public services are failing is the rolling austerity that promotes a vicious class war against Britain's poor. Without the labour, skills and dedication of migrants staffing the NHS and other public services, those public services would have collapsed."

Echoing a report by MPs last week, which complained both sides were knowingly misleading people with their figures, Varoufakis said the Remain campaign and Brexiteers were "infantilising voters in a cynical and astonishing fashion".

Green MP Caroline Lucas told the rally the left had been “too quiet” for too long on the EU.

She said: “Europe needs to be more democratic, accountable and transparent - but so does Westminster. We need to be in it to change it."

A quarter of the 14m people under-35 have still not registered to vote in the referendum, leading to a danger of Brexit by default, Ed Miliband warned at a different event.

Urging young people to register before the June 7 deadline, the former Labour leader said: “Young people can decide this referendum. If they don't use their vote, the danger is this referendum will be lost.”

Pro-Brexit Tory MP James Cleverly said Miliband’s “cynical” pitch would “fool no one”.

The Labour interventions came as the Tory feuding worsened, with employment minister Priti Patel claiming the immigration system under pro-Remain Home Secretary Theresa May was in “chaos” and trashing the Treasury’s economic forecasts.

Writing in the Sun, Patel said: “If the Government seriously believed the doom-laden propaganda they have been pumping out about the horrors of life after the EU, they would never have called this referendum in the first place.

“The Government thinks it can predict what will happen in the economy in 2030. Last November, the Treasury said there was going to be a windfall of £27bn. When the Budget came round in March, that had turned into a £56bn shortfall. Fourteen years ahead? They can't even predict 14 weeks ahead."

Former Tory party chairman Chris Patten also claimed leading Outer Boris Johnson “can’t understand the difference between fact and fiction” and “just makes it up as he goes along”.

Humza Yousaf, director of the SNP in Europe campaign, launched a “national weekend of action” highlighting EU safeguards on workers’ rights, civil liberties and consumer protection.

MP Stephen Gethins, the SNP’s Europe spokesman, complained to Vote Leave after it used his picture and words on its leaflets without permission to promote an Out vote.

Gethins said his comments, including one that the UK could survive outside the EU as much as Scotland could survive outside the UK, had been put in an “extraordinarily misleading” context.

READ MORE: The Tory party is disastrously split over Brexit – and the real fight begins on June 24

He said: “We should treat this debate with the seriousness it deserves.”

Scottish Labour leader Kezia Dugdale highlighted the £340m Scotland had received for apprenticeships and skills over the last decade from the European Social Fund.

The latest UK poll of polls puts Remain on 46 per cent, Leave on 42 per cent and Don't Know on 12 per cent.