Boris Johnson has rejected conspiracy claims levelled against Leave campaigners, arguing there is "considerably better" evidence proving the Loch Ness Monster exists than the Government's Brexit forecasts.
The former London mayor bemoaned the "colossal, glutinous tide of nonsense" from Remain as the campaigns continued to belittle and discredit the increasingly frenetic warnings they have issued ahead of next month's referendum.
Mr Johnson's remarks came as Vote Leave attempted to move attention onto concerns over the ability of the UK to deal with tax avoidance while Britain remains in the EU.
They claim the NHS and other services have been denied investment as EU rulings have helped multinational businesses "avoid paying billions" in taxes in the UK.
But these warnings followed a second day in which questions and concerns were raised over Mr Johnson's comparison of the EU with Nazi dictator Adolf Hitler's plans for domination of the continent.
George Osborne also accused the Leave camp of treating economic warnings as a "massive conspiracy".
The Chancellor added: "The next thing we know, the Leave camp will be accusing us of faking the moon landings, kidnapping Shergar and covering up the existence of the Loch Ness monster."
But Mr Johnson hit back and mocked the reliability of the research issued by the Treasury in support of Britain remaining in the EU.
During a visit to Nottingham, he told reporters: "It's bit rich from those who said World War Three will break out if we leave the European Union and the economy will fall off a cliff.
"I'm concerned there is now so much talking down of the UK that it's positively counter-productive. It's ludicrous.
"The Prime Minister before the renegotiations in Brussels was saying there was no question we'd get a fair trade deal, he said he was perfectly prepared to walk away - what's changed?"
Later asked if the moon landings were faked, Labour MP and Vote Leave chairwoman Gisela Stuart joked: "The ones with Elvis Presley? Yeah, those were."
Mr Johnson replied: "They were about as reliable as Treasury forecasts."
Questioned if the Loch Ness Monster exists, Mr Johnson joked: "The evidence for the Loch Ness Monster is considerably better than Treasury forecasts."
On the Hitler remarks, Mr Johnson was pressed to say whether he would make them again if he knew the controversy it would cause.
He noted: "Previous attempts to unify Europe have been done by force and have ended tragically. There are various historical illustrations of that point, which need no elaboration.
"What the Roman Empire had and the EU doesn't have is a single pole of authority that everyone understood and recognised and felt an allegiance to. That was the crucial point.
"Under the Roman Empire, people felt Roman. Under this European system, nobody actually feels European - some people might do, but very few people do, and that is the core of the problem."
Mr Johnson also blamed EU regulations for benefiting a minority of businesses who can deal with policy makers while freezing out others, adding the increasing gap between the pay packets of FTSE 100 chief executives and lower-paid staff is "nauseating".
The Vote Leave battle bus tour will continue on Tuesday in the Midlands, with Mr Johnson and Ms Stuart attempting to switch the focus on to their campaign's belief that the EU is hampering efforts to tackle tax avoidance.
It is relying on estimates from a 2011 Government document to suggest reforms to rules related to foreign subsidiaries of British companies, following a European Court ruling in 2006, have reduced corporate tax revenues by £2.36 billion since 2012.
The Leave camp has also raised concerns about the effectiveness of the diverted profits tax, which was introduced in 2015 to impose levies at a higher rate on sums believed to have been shielded from corporation tax.
Ms Stuart said: "The EU's rulings have helped multinational businesses to avoid paying billions in taxes here in the UK.
"That's money that could be invested in our NHS.
"The best way to stop big businesses from avoiding tax is to Vote Leave so we can take back control and reintroduce a fair system that works for the British taxpayer not big business."