The UK government is talking up Brexit opportunities around the globe but at the moment it is the great unknowns that are causing concern. Among them is what happens to the UK’s participation in the EU’s open-skies arrangement, under which any European airline can fly between two points in the bloc.

Officials speak of potential for new bilaterals between the UK and non-EU countries. However, it is vital that access to the internal air transport system is maintained. This particularly affects Europe’s two low-cost titans. The UK’s EasyJet operates hundreds of flights a week that never touch its home country, while Ryanair – based and registered in Dublin – has its biggest customer base on the other side of the Irish Sea.

Both countries have fall-back plans – Ryanair to establish a subsidiary for UK domestic flights and EasyJet an air operator’s certificate in an EU country that would allow it to continue offering intra-Europe services.

Much depends on whether the UK achieves a “soft Brexit” – retaining its membership of the single market – or the “hard” version that would force London to ­negotiate all its trade arrangements anew.

For all the talk of opening up the world, the latter would create a bureaucratic brain-ache for airlines at best. At worst, it would destroy the liberal aviation environment painstakingly created over recent decades, and – along with it – low fares and consumer choice.