EU referendum: Osborne accuses Leave camp of 'conspiracies'
Chancellor George Osborne has accused Leave campaigners of indulging in conspiracy theories in their response to economic warnings about an EU exit.
He said they would be accusing the Remain camp of "faking the moon landings" next, as he claimed an EU exit would risk £200bn a year in trade.
He was sharing a platform with former political foes Ed Balls and Sir Vince Cable who are backing the Remain cause.
The Leave campaign accused Remain of resorting to "lurid scare stories".
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Vote Leave, meanwhile, was backed by 306 business figures who signed a letter published in the Daily Telegraph,.
Voters will be asked to decide whether they want the UK to stay in or leave the European Union on 23 June.
In a speech at Stansted Airport on Monday, Mr Osborne unveiled what were billed as surprise guests, Ed Balls and Sir Vince Cable, as he warned that it would be a "huge mistake" to quit the EU.
He said leaving the single market - in which there are no tariffs, quotas or taxes on trade and where there is free movement of goods, services, capital and people - would cost Britain £200bn in a trade a year - as well as £200bn overseas investment.
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"There is a reason the three of us are standing here today putting aside our political differences," said the chancellor.
"It's not a conspiracy, it's called a consensus," he said, adding: "Britain will be worse off if we leave the EU."
Mr Osborne said the economic consensus that had emerged, that "Britain will be poorer" outside the EU, was shared by organisations including the International Monetary Fund and the Bank of England and by figures including US President Barack Obama.
But he said the Leave camp "say it is all a massive conspiracy" and claim it is "all 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," he said.
By BBC Political Editor Laura Kuenssberg
Just as the chancellor is trying to claim victory in the economic debate his colleagues on the other side like Boris Johnson are digging in, characterising the debate as nothing less than a struggle between fat cats and the common man.
George Osborne can claim the economic debate is over, but voters will decide who and what they want to hear.
Responding to Mr Osborne's comments, Conservative cabinet minister and Vote Leave campaigner Chris Grayling told 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."
This would leave Britain "on the fringes, with them making our laws for us" and the UK would not be able to do anything about it, Mr Grayling said.
In reference to the IMF's warning, he said the organisation had got its economic forecasts wrong in the past and it was "getting it wrong now", and claimed its chief, Christine Lagarde, was an "avowed, devoted Euro federalist".
But former Labour shadow chancellor Ed Balls - once described by David Cameron as "the most annoying person in modern politics" - said the EU single market had been "great" for consumers while Sir Vince, Lib Dem business secretary under the coalition, said British businesses and workers "stand to lose substantially" from leaving.
Ryanair chief executive Mr O'Leary said the company was creating 450 new jobs in Britain as part of the $1.4bn it invests in the UK - but he warned this could have to be scaled back if the UK left the EU.
He also said it was a "certainty" that air fares and the costs of holidays would rise - although he has previously said ticket prices would not be affected by an EU exit and in 2004 described the EU as an "evil empire".
In February, he told ITV News: "I don't believe leaving the European Union will cause air fares to rise. The thing that will drive up air fares in Britain is the UK government's travel tax."
Vote Leave chief executive Matthew Elliott said: "George Osborne appeared today alongside one man who thinks that the EU is an evil empire and another who said that the chancellor does not understand economics.
"George Osborne is panicking about his failing campaign so he is resorting to ever more lurid scare stories."
Meanwhile, signatories to the letter backing Vote Leave include Superdrug founder Peter Goldstein, former Sony vice-president Steve Dowdle, Goldman Sachs managing director David Sismey, Tim Martin, chairman of pub chain JD Wetherspoon and Adrian McAlpine, from construction firm Sir Robert McAlpine.