Boris Johnson accused of 'nasty game' by comparing EU to Hitler superstate plan

Read more: Corbyn: Sharing stage with PM would make 'good television' but will not happen

Mr Johnson - seen as the de facto leader of the Leave campaign - said the past 2,000 years of European history had been dominated by doomed attempts to unify the continent under a single government to recreate the "golden age" of the Romans.

"Napoleon, Hitler, various people tried this out, and it ends tragically. The EU is an attempt to do this by different methods," he said in an interview with The Sunday Telegraph.

"But fundamentally what is lacking is the eternal problem, which is that there is no underlying loyalty to the idea of Europe.

"There is no single authority that anybody respects or understands. That is causing this massive democratic void."

His comments were immediately condemned by the Britain Stronger In Europe campaign, with Labour former cabinet minister Yvette Cooper accusing him of playing a "nasty, nasty game".

"The more he flails around with this kind of hysterical claim, the more he exposes his shameful lack of judgement, his willingness to play the most divisive cynical politics, and the emptiness of his arguments," she said.

"One week it is dog whistle attacks on President Obama. Now he is trying to liken the institution that has kept peace on our continent for decades with Hitler, who pursued the genocide of millions of innocent people.

"All because he is desperately seeking headlines for a desperate campaign. He should not try to play political games with the darkest and most sinister chapter of Europe's history.

"The EU has played a critical role keeping peace in Europe ever since."

The row erupted as Nigel Farage backed Mr Johnson to succeed David Cameron if there is a vote to leave the EU in the referendum on June 23.

The Ukip leader described himself as a "Boris fan" and compared him to former US president Ronald Reagan.

In comments clearly designed to stoke tensions within the Conservative Party over the referendum, Mr Farage said he could even envisage a situation in which he could work for Mr Johnson in government.

Mr Cameron has always insisted that he will carry on regardless of the result, but many MPs believe he will have no choice but to resign if the country rejects his call to Remain.

In an interview with The Mail On Sunday, Mr Farage rejected suggestions that Mr Johnson was not serious enough to be prime minister if Mr Cameron was forced to stand down.

"Boris goes on surprising people. They say he can't do this, he's a joker - it's like Ronnie Reagan. Could he do it? Yes. If you'd asked me six months ago I'd have said no but I've changed my mind," he said.

Asked if he would like to work for Mr Johnson if there was a vote for Leave, Mr Farage said: "I love Boris, respect him, admire him; I'm a Boris fan.

"Could I work for him? Yes. Could I see a scenario if he was PM and he asked me to do something? I wouldn't rule it out."

Mr Farage brushed aside the objections of the official Vote Leave campaign that he had been chosen by ITV to take on Mr Cameron in their televised debate rather than one of Vote Leave's big names like Mr Johnson or Michael Gove.

"They're terrified if I play a big role, what happens after the referendum, could I nick a third of their voters?" the Ukip leader said.

He also indicated he was preparing to ramp up his rhetoric on immigration despite what he said were "idiotic pleas" to "tone down" his comments for fear of alienating moderate voters. "You ain't seen nothing yet," he said.

While Mr Johnson has consistently argued that "uncontrolled" immigration into the UK was too high, campaigning in Bristol on Saturday he stressed he was not anti-immigration.

"I am in favour of immigration, I'm a believer in it," he said. "What is not right is for huge numbers to come here in a way politicians say is not going to happen. That's where I part company."

Shadow foreign secretary Hilary Benn said Mr Johnson's comparison of the EU to the Third Reich was "offensive and desperate".

"Leave campaigners have lost the economic argument and now they are losing their moral compass," he said.

"After the horror of the Second World War, the EU helped to bring an end to centuries of conflict in Europe and for Boris Johnson to make this comparison is both offensive and desperate."

Labour leader Jeremy Corbyn told ITV's Peston On Sunday: "Boris Johnson has some very odd interpretations of history.

"I think he actually needs to take some lessons from Jacob Rees-Mogg because he's a better historian than Boris Johnson."

Mr Corbyn joked: "I don't want to cause any dissent within the Tory party but you've got one better historian than the other. They may fall out over this."

Tory MP Mr Rees-Mogg described Mr Johnson's remarks as a "very interesting historic parallel", earlier telling the same programme: "What Boris was saying is absolutely true.

"Philip II of Spain, Louis XIV of France, Napoleon and Hitler all wanted to create a single European power.

"What Boris has said is the EU is following the footsteps of these historic figures but using different means.

"Now, all of those tried to do it by force and the EU is trying to do it by stealth, and whenever there's a vote that goes against them they make people vote again or, as quite disgracefully in Greece, they simply ignored the vote altogether."

Former Liberal Democrat leader Lord Campbell said Mr Johnson's comments showed his unsuitability for high office.

"Not content with insulting the President of the United States, he now grossly misrepresents the history, aims and objectives of the European Union which was founded to enshrine democratic values and to prevent a repeat of the fascism which polluted the continent under the Nazis," he said.

Conservative former chancellor Lord Lamont said it is a "fact there were fascist theorists who believed very strongly in a united Europe".

He also said the headline for Mr Johnson's comments was "misleading".

Lord Lamont told Murnaghan on Sky News: "I don't think (Mr Johnson) was saying people who favour the European Union were comparable to Nazis.

"He was simply saying that historically, from the Romans, Charlemagne, Napoleon, there have been all sorts of attempts to dominate Europe and these have all floundered because Europe is not naturally one entity."

Asked if Mr Johnson's remarks were helpful to the Leave campaign, Lord Lamont said: "I don't actually think what he said, as it was said, was so outrageous. I think the headline is misleading."

Pressed if he wished Mr Johnson had not made the comments, Lord Lamont said: "I myself referred not so long ago but was very careful to say, 'I'm not comparing people who support Europe to Nazis', but it actually is a fact there were fascist theorists who believed very strongly in a united Europe."

Mr Johnson's comments were defended by the pro-Brexit former cabinet minister Iain Duncan Smith who said he was simply stating a "historical fact of life".

"I think the whole process of trying to drive Europe together by force or by bureaucracy and democratic means ultimately makes problems," he told BBC One's The Andrew Marr Show.

"All he is doing in the interview is he is talking about the trend towards the idea of this kind of concept of some kind of greater Europe, that's all."