I asked a similar last Oct
http://www.pprune.org/forums/showthread.php?t=194158wondering if my Irish issued JAA PPL would allow me to fly at night in the UK, given that I (or anyone else) was not allowed fly an Irish registered aircraft under IFR, unless they held an instrument rating, according to Irish Regulations.
No one was able to quote anything that made me think that I would be allowed fly at night in the UK, in an Irish registered aircraft.
Interestingly, I sent the CAA an email (as someone suggested I should do), and the only reply I got, was an email acknowledging my query.
On the face of it, it seems a similar enough position to the FAA licence holder + N reg aircraft, in the UK at night (although I know very little about the FARs).
While I'm sure that no one could care less, so long as there was no incident, I'm not so sure people wouldn't mind, if there was some sort of incident.
dp