British and European Union airlines would lose the automatic right to fly to each other’s territories if there is no Brexit deal, the government said.
The warning was contained in technical guidance about Brexit released by ministers on Monday.
The government wants both sides to mutually recognise EU and UK aviation standards ahead of Britain’s departure.
However, the EU has not yet done so and will stop recognising UK safety practises on the day of a hard Brexit.
“If the UK leaves the EU in March 2019 with no agreement in place, UK and EU licensed airlines would lose the automatic right to operate air services between the UK and the EU without seeking advance permission,” the government said.
The warning does not necessarily mean that flights would be grounded the day after Brexit.
According to Airlines UK, which represents 13 UK-registered carriers, the European Commission has said it would put in place a “bare bones” aviation agreement with the UK to keep planes flying and to cover safety issues.
Tim Alderslade, the trade body’s chief executive, said airlines expected the EU and UK to reach a new agreement on aviation.
“Whilst we don’t support a no-deal Brexit, we welcome that both the UK and the EU are proposing in this event a minimum agreement that would cover flight and safety requirements for the benefit of both passenger and cargo services,” he said.
ADS Group, which represents the UK’s aerospace, defence, security and space sectors, has called for Britain to remain a member of the European Aviation Safety Agency (EASA).
It said talks should be held between the Civil Aviation Authority and the EASA to address the complex issues involved and ensure flights are not disrupted.