Boris Johnson has dismissed the "hysteria" over his comparison between the European Union and Hitler's plans for domination of the continent.

The prominent Leave campaigner claimed the row over his comments was an "artificial media twit storm".

But Chancellor George Osborne endorsed the view of former military chief Field Marshal Lord Bramall, who described Mr Johnson's remarks as "simply laughable" and "absurd".

Mr Johnson - seen as the de facto leader of the Leave campaign - said the past 2,000 years 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.

Challenged about his comments on Monday, he told the BBC: "This discussion is bedevilled by all sorts of artificial media twit storms and hysteria of one kind or another.

"There is a very good argument against the lack of democracy in the EU. Over the last 2,000 years people have made repeated attempts to unify Europe by force, the EU is a very different project but it is profoundly anti-democratic and that is why we should vote Leave on June 23."

Mr Osborne, speaking at a Remain event in Stansted Airport, said: "As someone who studied history at university, you always go to the first-hand sources. Yesterday we had Lord Bramall, who was a field marshal in the British Army, who himself as a young man landed on the beaches on D-Day to fight and defend our country.

"I think he said what needed to be said about Boris Johnson."

Former chief of the defence staff Lord Bramall said: "I know only too well, this comparison of the EU and Nazi Germany is absurd."

Labour former cabinet minister Ed Balls, who was sharing a platform with his former political sparring partner Mr Osborne, said Mr Johnson's comments were "ill-judged and irresponsible".

He said: "I think it is clearly attention-seeking, he is trying to distract attention from the big issues. From my point of view it shows a massive lack of judgment."

A Downing Street spokesman said: "The Prime Minister disagrees with the comments.

"As he set out in a speech last week, he believes the EU plays a vital role in preventing conflict in Europe. He pointed to the fact that the EU has helped reconcile countries which were once at each other's throats for decades and that we have a fundamental national interest in maintaining a common purpose in Europe to avoid future conflicts."

The spokesman added: "The PM is making his arguments for why we should remain very forcefully. He respects the views of others and their right to make those views known, but he believes that we are stronger, safer and better off in the EU."

Asked about Lord Bramall's comments during a campaign visit to Alfreton, Derbyshire, Mr Johnson said: "I think it's very important that we should continue to point out that the EU is fundamentally anti-democratic and getting less and less democratic.

"People on my side of the argument have got to continue to point that out and it's absolutely vital that we understand of course the EU is a peaceful organisation, everybody understands that, but it's operating by stealth and taking away the powers and prerogatives of the people of this country - above all our right at elections to decide who runs this country."

He said he welcomed a "lively discussion" in the EU referendum debate, adding: "People can't be told to shut up about this or that when they care very much about democracy in this country, I think we all have a right to speak out."

Vote Leave chairwoman and Labour MP Gisela Stuart, who was born in Germany, was asked if she believed it was tasteful for Mr Johnson to refer to Hitler in the debate.

Ms Stuart replied: "I'll tell you what I think is important - that we remind a whole generation that has never had an opportunity to have a say as to how itself it wishes to be governed, and the relationship it wishes to have with other nation states in Europe, that they should actually be given some facts, that we should go back to the debate.

"I think this company here today, these are people who are producing goods which the whole of Europe wishes to buy but not under the constraints we have, and I think we'd all benefit, including our democracy, to go back to what the referendum is about."

Ukip MEP Gerard Batten defended Mr Johnson's comments, arguing that Hitler's Germany had drawn up plans for a European economic community during the Second World War and that the European Commission's first president Walter Hallstein had fought in the German army and been a member of "several nominally Nazi professional organisations".

In his blog, Mr Batten wrote: "In 1942 when the Germans still thought they were going to win the war they produced a report entitled the Europaische Wirtschaftsgemeinschaft - which translates as the European Economic Community.

"This report was written by various bankers and academics and laid out a plan for how Germany would manage the economies of the conquered countries of Europe after a German victory.

"The report was drawn up under the leadership of Professor Walter Funk, the Reich's economics minister and president of the Reichsbank.

"The report contained sections on agriculture, industry, employment, transport, trade, economic agreements and currency. It proposed the 'harmonisation' of European currencies and a harmonised currency system.

"If this all sounds all very familiar it is because the basic plan for the European Economic Community of 1942 was very similar to the actual European Economic Community that came into existence in 1957 under the Treaty of Rome."