Just correct me if I am wrong , but Overflight right are old ICAO and Chicago stuff.
At no point can UK close airspace or overcharge any EU operator if a Hard Brexit is in place april 2019. Or if a Dumb Brexit is entered in April!
( A Dumb Brexit is a Hard Brexit with no plan or deal signed before 01:00 1 April 2019 Brussels Time! )
Anyone suggesting restrictions in UK airspace must be a moron. EU would use one nano second to retaliate and any Eastbound UK flight would face a new departure slot two to 5 years down the road. I can fly around the UK any time, but try avoiding European Airspace?. It goes from the North Pole to Africa!
Remember UK airspace is tiny and has no effect on 90% of European flights. So who cares!
I think it is only FAA that has taken this situation seriously, by sending over Inspectors. Interesting indeed.