I have a friend who has failed his JAA medical

, but passed his FAA medical

.
He does though, have a JAA microlight, and appropriate licence.
He is asking if he can:
Go to US and get his FAA PPL.
Come back here, and fly a G registered aeroplane in the UK using his FAA PPL.
My gut feeling is yes - but I am not sure.
Additionally, I suspect he can probably use his FAA PPL with a G registered aeroplane, and fly it around Europe (subject to individual countries giving him the okay - as per the other post about this).
Am I missing a key piece of the puzzle?
Safe flights, Sam.