Grob,
I used to fly G-HUEY on behalf of Rob Tierney and the RAF Benevolent Fund, before those (insert suitable vehement epithet of your choice here...)s at IAT stitched him - and us - well-and-truly. You can forget operating the Bell 204/5 on a UK PT Certificate, the CAA blocked that back in the early days. Although I believe the reason given is that the aircraft has only one hydraulic system (which most of us could easily cope without for one landing), the real motive was probably to protect the European heli manufacturers from a mass dumping of surplus US Hueys after Vietnam. G-HUEY was operated on a restrictive Permit to Fly; Bristows very kindly undertook supervision of the engineering. Can't give you an answer on the N-reg thing.