BRUSSELS: Britain's aviation sector could see severe disruption in the medium-term if it leaves the European Union without a withdrawal agreement, Ryanair chief executive Michael O'Leary warned on Wednesday.

"There are measures that are being put in place both by Europe and the UK that would prevent enormous disruption over the first 9 or 12 months but after that if there is a hard Brexit and no trade deal there could well be severe disruption," O'Leary told journalists in Brussels.

"We still hope that some kind of common sense will prevail in the UK although there is precious little of it at the moment," he said.