Chancellor George Osborne has accused the Leave camp in the EU referendum of indulging in conspiracy theories, as he insisted that there was an "overwhelming consensus" among economists and world leaders that Brexit would be bad for the UK.
Mr Osborne was speaking alongside Ryanair boss Michael O'Leary, who warned that withdrawal from the EU would force up the price of flights and holidays and put his company's latest £1 billion investment in the UK at risk.
But Vote Leave campaigners dismissed Mr Osborne's comments as "lurid scare stories" which would not be seen as credible by voters taking part in the June 23 referendum.
Meanwhile, more than 300 business leaders signed a letter urging Britain to vote to leave the EU, warning that the UK's competitiveness is being undermined by its membership.
And the pro-Brexit ex-mayor of London Boris Johnson hit the road again in his battlebus, visiting Alfreton in Derbyshire amid controversy over his comparison between the EU and the dreams of pan-European government pursued by Napoleon and Hitler.
Second World War veteran and former chief of the defence staff Lord Bramall dismissed the comparison as "absurd", while Labour's former cabinet minister Ed Balls said the comments were "ill-judged and irresponsible".
But Mr Johnson brushed off the criticism, insisting the EU was "fundamentally anti-democratic" and was " operating by stealth and taking away the powers and prerogatives of the people of this country". He was defended by Ukip MEP Gerard Batten, who said the European Economic Community established in 1957 was "very similar" to a proposal drawn up by officials in Hitler's Germany.
Mr Osborne was joined by Mr Balls and Liberal Democrat former business secretary Sir Vince Cable at Stansted Airport to make the case for a Remain vote in front of a Ryanair Boeing 737 emblazoned with the slogan "stronger, safer and better off in Europe".
The Chancellor said Treasury analysis showed that if the UK was forced to rely on World Trade Organisation rules following Brexit, it could expect to lose trade worth £200 billion a year and overseas investment worth £200 billion within 15 years.
"Credible" observers ranging from the Bank of England and the International Monetary Fund to the OECD and US president Barack Obama had judged that "Britain will be poorer and British people will be poorer" if the UK votes to leave the EU, said the Chancellor.
But he said the Leave camp treated the warnings as "a massive conspiracy", implying that a series of international organisations and world leaders were part of "some global stitch-up to give misinformation to the British people".
"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," said Mr Osborne.
"The response to the sober economic warnings from around the world by those who want to leave the EU has not been credible or serious."
Mr Osborne added: "It's not a conspiracy. It's called a consensus. The interventions of the last couple of weeks, from the IMF to the Bank of England, make very clear that the economic argument is beyond doubt - Britain would be worse off if we leave the EU, British families will be worse off, equivalent to £4,300 a household.
"Leaving the EU is a one-way ticket to a poorer Britain."
Announcing the creation of 450 new jobs in Britain as part of a 1.4 billion US dollars (£976 million) investment in Ryanair bases, Mr O'Leary warned: "It is exactly this type of investment that will be lost to other competitor EU members if the UK votes to leave the European Union."
It was "a certainty" that the cost of flights and holidays would rise if the UK leaves the single market, he said.
But pro-Brexit Cabinet minister Chris Grayling dismissed Mr Osborne's claims, telling BBC News: "The reality is there's no conspiracy here at all. In fact, the conspiracy theories around the European Union are there in black and white, you don't need any hidden elements to it - there is a clear plan to create a federation of the eurozone."
And Vote Leave chief executive Matthew Elliott highlighted Mr O'Leary's previous criticism of the European Commission as an "evil empire".
"George Osborne is panicking about his failing campaign so he is resorting to ever more lurid scare stories," said Mr Elliott.
"His problem is that he's told so many tall tales that people no longer believe what he and David Cameron say on the EU any more."
The Leave.EU campaign noted that Mr O'Leary suggested last week that the "extreme volatility" which would follow a vote for withdrawal from the EU could force air fares down, in the same way they fell after the September 11 terror attacks in 2001.
Arron Banks, co-chairman of Leave.EU, said: " Low costs and high wages are obviously bad news for the big bosses at multi-nationals like Ryanair, but they're great news for ordinary people.
"Add in the return of duty-free when travelling to EU countries, and Brexit looks like a great deal all round for British travellers."
Signatories to the pro-Brexit business letter included Peter Goldstein, a founder of Superdrug; Steve Dowdle, a former vice-president Europe of Sony; David Sismey, a managing director of Goldman Sachs, and Sir Patrick Sheehy, the former chairman of British American Tobacco.
"Brussels's red tape stifles every one of Britain's 5.4 million businesses, even though only a small minority actually trade with the EU," they said.
Mr Johnson likened statements of support for the Remain campaign by high profile figures and business chiefs to "hostage videos".
He told the BBC: "People very often don't understand when they see these Downing Street hostage videos of these people coming through Downing Street and giving these endorsements of the Remain campaign, what they don't understand is that actually they're not speaking for the vast majority of British business."