The UK aviation industry could “fall off a cliff” in two years' time because of the decision to leave the European Union, Ryanair boss, Michael O’Leary has warned.

Mr O’Leary said he fears that Prime Minister Theresa May’s plan to leave the EU single market could result in UK airlines losing access to the EU's deregulated aviation market, Reuters reports.

"We worry that the price of remaining in Open Skies will be the UK accepting freedom of movement of people ... I think that may be unlikely, in which case we may be heading for a very hard Brexit," O'Leary told journalists in Dublin.

“We don't think it is possible to get interim arrangements through 27 European parliaments in a two-year period, so the British will fall off a cliff in two years' time," Mr O’Leary said.

The Open Skies agreement, introduced in 1997, allows any EU airline to fly between any two airports in Europe. It has been key to the rise of budget airlines such as Ryanair. The Irish carrier is now the largest in Europe by passenger numbers, with a third of those trips departing from UK airports.

Mr O’Leary also warned that uncertainty around Brexit could affect demand across the continent.

"There will be slower UK growth but also slower European growth," he said, adding that a hard Brexit would be "a catastrophe for the UK economy but also for neighbouring economies".

The airline boss, who campaigned strenuously for the Remain vote during the EU referendum, has repeatedly lambasted the Government for its lack of clarity over Brexit.

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In November 2016 he told the Airport Operators’ Association the UK would be “screwed to the floor” during negotiations and likened ministers to the cast of Dad’s Army. “The politicians have no idea how they are going to exit the EU”, he said.