In a ‘notice to operators’, the European Commission in Brussels has warned that UK carriers will no longer enjoy freedom of the airways after March 30 2019, when Britain leaves the EU.

The letter goes on to spell out the consequences if no agreement is reached or if they do not gain an EU licence - for example by moving their head office to mainland Europe. It says: “As of the withdrawal date, the operating licences granted to airlines by the United Kingdom Civil Aviation Authority will no longer be valid EU operating licences.”

It adds: “Air carriers are advised to consider any measure required to ensure that the conditions for holding an EU operating licence are complied with in all circumstances.”

The EC also warns that air traffic rights will cease and adds: “Preparing for the withdrawal is not just a matter for Union and national authorities, but also for private parties.”

The industry body Airlines UK said the notice was one of several issued to other sectors, “not just air transport”. It added: “We believe it is simply part of a wider process on publicly setting out the legal position and the EC’s stance ahead of moving to stage two of discussions later this week – assuming they agree to move on from stage one.”