WW2 Royal Air Force war workers numbered official identification badge

A scarce original wartime period 'Royal Air Force official identification badge'; circular nickel example, the centre bearing a King George VI Crown above a tablet with officially impressed issue number '1916', the reverse impressed with maker's details 'Dingley B'Ham'. Good condition, retaining original buttonhole fitting, minor service wear. Diameter 28mm. Worn as an official identification for civilians On Government Work serving on RAF Airfields, etc.