Mine failed the MOT on it being in the front window so screwed in on the front bumper, so now its nicley covered by winch hook.
one of the landy mags was asked this question recently and the answer was that the number plates must be fitted to the "front" of the vehicle and the mag sugested it meant the furthest front rather than just forward facing but there was no difinitive answer.
all new numberplates must have suppliers name and postcode on it.