Ryanair boss Michael O'Leary has warned there is a remote chance of all flights between the UK and Europe being suspended in March 2019 if the UK Government opts for a "cliff-edge" Brexit.
The businessman said the current open skies arrangement hinges on recognising the jurisdiction of the European Court of Justice, which Prime Minister Theresa May said Britain would no longer be subject to.
Mr O'Leary believes it will take more than the two-year time frame from triggering Article 50 to put agreements in place with European Union (EU) nations.
He said: "In the airline industry we could be heading for a very difficult divorce with Europe.
"There is a possibility, unlikely, but nevertheless a possibility that there may be no flights between the UK and Europe in March 2019 if the UK walks off this cliff that they seem determined to walk off."
The airline head said he was switching growth plans away from the UK and would not create any more pilot or cabin crew posts, or increase the amount of planes there due to Brexit uncertainty.
He said new routes announced in Scotland on Thursday would use planes based elsewhere in Europe and would move to other European countries in the event of a hard Brexit.
Mr O'Leary accused the UK Government of being clueless over Brexit and hoped that the UK would stay in the EU.
He said: "Brexit - no exit plan by the UK Government. I don't think they have a clue what they are engaged in.
"I've had a number of meetings in London in recent weeks where they are going to do a great deal for Britain, and then I got to Frankfurt and Brussels and Paris where they are determined to do Britain down, and I fear they will.
"We have to recognise the will of the the people, they did vote in a referendum, however they were fundamentally misled into believing they could leave Europe and nothing would change.
"Everything is going to change, and probably for the worse."