Asked by analysts about the location of cuts planned in the coming months as a result of delays in the delivery of the Boeing 737 MAX, O'Leary said routes from London to Glasgow, Edinburgh and Belfast would be obvious candidates.

"An obvious one (to cut) if there is a hard Brexit at the end of October, we have three UK domestic routes... They would readily fall out straight away," he said.

"There is a longer-term question mark over those in a hard Brexit," O'Leary said. "Frankly ... we are not growing in Edinburgh, Glasgow or Belfast.