Ryanair boss Michael O'Leary has predicted that air fares will fall by as much as 15 per cent over the winter, as airlines compete to win passengers in a slow economy.
O'Leary said there would be "extraordinary fare declines" over the year, after reporting results for the first half of the year.
The budget airline's average fare fell 10 per cent in the six months to the end of September, partly due to the conversion of sterling fares, which account for a quarter of its revenues, into euros. It has forecast average fares dropping 13-15 per cent in the six months to the end of March.
O'Leary also warned that if carriers do divert services away from Britain due to uncertainty over aviation regulations following the Brexit vote, less competition would mean prices rise again.
"There will be lower capacity in the UK until someone can tell us what Brexit means," he said. "Passengers will get lower fares over the next 18 months. But if there is a hard Brexit, there will be less capacity in the UK and less capacity means higher prices."
He also expressed concern over whether the ministers would be able to secure an "open skies" Single Market settlement for the aviation industry.
"I think it is a shambles, but long may it remain a shambles until they realise that they can't leave the Single Market," he said.
Ryanair's chief executive has been a vocal critic of leaving the EU and yesterday said Theresa May was "faffing about" in India, when she should be focusing on arranging trade deals with Brussels.
The company had confirmed a lowering of profits expected for the current financial year, but upgraded its longer-term forecast to carry 200m passengers in 2023-24.