Ryanair's chief executive Michael O'Leary has ramped up his warnings of a no-deal Brexit, saying the UK had received "no assurances" from the EU that flights could continue after Britain leaves the bloc.
He said the transport secretary, Chris Grayling, had received "no assurances" from the EU on continued flying, and that the likelihood of a no-deal Brexit was growing.
"If it's not a 21-month transition period, the thing that is not being well explained by the Brexiters is that flights to and from the EU will be stopped in a hard Brexit," O'Leary said. "Chris Grayling has yet to explain what else is going to be put in its place."
While he was confident the UK would reach a deal with the EU on flying rights, it would "not be in time for 1 April next year if there is a hard Brexit".
"If you look at the behaviour of the Europeans the 27 have remained united," the boss added.
O'Leary warned earlier this year that flights could be grounded in March 2019, the deadline for when the UK leaves the EU.
If that happened a no-flights scenario would not last longer than "two days or two weeks", he added, but no longer because it was "politically unsellable".
"Even the crazier wing of Brexiteers will struggle to say why there are no flights," O'Leary said.
A Department for Transport spokesperson said: “Aviation is absolutely crucial to the UK’s economy and we are committed to getting the best deal possible for Britain.
“We believe that it is in the interests of both sides to ensure continuity – but it is only sensible to prepare for a range of scenarios.
“That is why, as the Commission will not yet engage with the UK on contingency planning, we have proposed bilateral conversations with Member States to discuss arrangements we could put in place to ensure continued air connectivity.”