Delegation of control for FIRs over the high seas is an ICAO issue, nothing to do with the EU or EASA. However, pithy one-liners aside, if there was a real p1ssing contest it could get tricky since although control is done by the UK from Prestwick all the comms go through RoI at Ballygireen. NAT region closed to everyone would probably result in a US invasion of Europe to knock everyone's heads together...
