Five million airfares could be cancelled on the tarmac in the event of a “no-deal Brexit”.

However, airline operators have been accused of being “unwilling to produce information” about the consequences of an uncoordinated United Kingdom exit from the European Union.

The International Air Transport Association (IATA) said as many as five million tickets were “at risk” should negotiations not produce a deal.

Rory Boland, the editor of UK consumer rights magazine Which? said “the lack of warning for passengers is alarming”.

In an interview with The Times of London, Boland said “It is the job of airlines to tell passengers what is likely to happen. If they were more upfront it would give passengers the information they need to protect themselves.”

Examining the booking process on websites belonging to UK airlines Boland’s publication found no warning of the potential risks to passengers’ journeys, even when booking flights on or after March 29, 2019 – the date when the UK is scheduled to cease to be a member of the EU, with or without a deal being negotiated.

What happens if your flight gets axed by Brexit?

Passengers with tickets that are cancelled by Brexit should automatically be given refunds.

IATA chief executive Alexandre de Juniac said: “That current flight levels will be protected even with a hard Brexit is an important assurance.”

A number of flights have been safeguarded by a cap agreed on during EU negotiations, which means for now air traffic will be protected at 2018 levels.

Although the IATA spokesperson admitted that there is still “legal and commercial uncertainty over how the Commission’s plan to cap flight numbers will work.”