I have also heard a whisper about this, but from the Department for Transport.......Maybe it is down to national security issues?? Something about an aircraft 'registered' in the USA, painted as such and operating over here, but not actually registered anymore with the FAA! Who's to know if it's actually registered apart from the FAA, who tend not to be looking much in the UK.
Lots of whispers together normally make a loud noise at some stage.