WPAS was taken from Wiltshire to Staverton by road just a few days before the general grounding, this may be it. I understand that it was an engine problem.
I have noticed before that PAS tend to obliterate the registrations of their road runners as part of the readying for the journey so this it not unusual.
As they left the aircraft titles untouched its nothing to do with secrecy. Perhaps someone thinks it may get mistaken for the registration number of the low loader if it jumped a red light!