Just to add to the complexity ..
A G reg aircraft cannot be used in EASA if paid for - commercial consideration, so becomes a commercial operation (not to be confused with CAT).
A UK examiner, holding both EASA and UK privileges, cannot examine a UK pilot in EASA in a EASA aircraft without approval from the EU state (airspace) where the flight takes place (according to the UK CAA).
Doesn't directly answer your question, but shows what a mess it is...