On His Majesty's Service Badge

Aircraft Inspection Directorate (AID) On His Majestys Service 102 mm (4") tall. Manufactured in brass and is 10 mm thick at the front of the Crown. Looks to be a test piece. Latest information is as follows :- These badges relate to the Air Ministry's "Aircraft Inspection Directorate" and similar patterns are found on the very much smaller lapel badges. A.I.D. offices were found in all British aircraft factories and these larger badges were positioned on the outer doors of these offices (attached by screws). Obviously similar designs could also have been produced as car grille badges for senior personnel, but I would suggest that they were more often door-plates. Thanks to Dave for the information