This is a great photo of several wardens and a messenger during a training exercise in Fulham in 1942. The wardens are all in serge battledress whilst the young messenger has a bluette overall on. Note the lamp hanging from the first aid haversack of the warden on the right (a WWI veteran wearing his ribbon). Also of interest is the Incident Officer lighting his cigarette. He is wearing the blue helmet cover and IO sleeve badge that denote his role at air raid incidents.
Photo from the IWM
News about interesting insignia, ARP related info and period photos that turn up.