A loco brand could have - and may well need - two subsidiaries, one in the UK & one in an EU country. You can then crew EU/UK flights with staff from the country where they are available. Switzerland is not part of the EU but is in the EEA and I suspect that very few easyJet pax will know or even care if an easyJet flight to/from GVA or Basle is operated by U2/EZY or DY/EZS.