No one is saying that UK aircraft would not be able to overfly European airspace. What they are saying is that UK aircraft will not be able to do domestic EU traffic or Eu-rest of the world traffic. Similarly EU airlines will not be able to do UK domestic traffic. Additionally all EU airlines need to be owned AND controlled by Eu nationals (easyjet? IAG?...) and Uk airlines will need to be UK owned AND controlled to take part in a new UK/US bilateral agreement (BA? Virgin?....)