European airlines are opposed to the UK getting "any favourable deal" to secure air routes after Brexit, Ryanair boss Michael O'Leary has warned.
The Dublin-based carrier's chief executive said EU airlines are "actively campaigning" for the UK to be offered a bilateral agreement which would be "almost unacceptable" to those in favour of a so-called hard Brexit.
The single market for aviation, created in the 1990s, means there are no commercial restrictions for airlines flying within the EU.
Mr O'Leary warned that flights between the UK and the EU will be grounded in summer 2019 if no deal is reached by September next year.
He told a central London press conference that he has seen briefing documents put out by airlines which call for any future flights to be under the jurisdiction of the European Court of Justice (ECJ).
Mr O'Leary said: " There's no doubt in our minds that the German and French airlines in particular are opposed to the UK getting any favourable deal.
"They are in favour and are actively campaigning for a bilateral with the UK under which the UK must accept ECJ jurisdiction, t hey accept all past and future regulation of air travel by the European a uthorities.
"(This) makes it almost unacceptable to those who believe here in a hard Brexit.
"They do not wish to be seen to bend the knee to the European Court of Justice or European regulations."
He said the airline logos on the documents include Lufthansa, Air France and KLM.
Mr O'Leary met Transport Secretary Chris Grayling on Wednesday to discuss the impact of the UK's withdrawal from the EU.
He said he stressed the need for an aviation agreement to be in place soon but is "more sceptical" than the Government that it will be possible.
"We think there's nobody on the other side that will be that willing to facilitate giving the British a great deal by September 2018," he said.
"There's huge upside for German and French airlines in disrupting British Airways flights between the UK and Europe, disrupting easyJet's flights... and causing us some grief that means we have to move planes out of the UK into continental Europe.
" If I was them I'd be doing exactly the same thing.
"If you can screw up your competition at reasonably little cost to yourself - they have very little capacity in the UK - then Godspeed."
Mr O'Leary told reporters that, if summer 2019 flights are cancelled, Britons will be left with "the option of driving to Scotland or getting the ferry to Ireland" for their holidays.
He joked that this will appeal to "all those many millions who like to go to Spain, Portugal and Greece for the cheap sunny holidays".
The Ryanair boss predicted that airlines will be "screaming blue murder" if there is no aviation agreement.