One thought is that this was not a Bedford but a Leyland Retriever as a Beaver-Eel (partly after Lord Beaverbrook) or 'Tender, Armoured Leyland Type C to the Royal Air Force', intended to protect factories from paratroop attacks. Well, they may have been originally but were collared for airfield defence and according to the official caption used in UK and North Africa. That said, a Leyland would not have Bedford running gear and details appear in Vauxhalls' archives! My guess was that this is a 3-ton OY Chassis built with the same body as the Leyland version. That front end rerminds of the Leyland and AEC Armoured Command vehicles. That made me do some research onn the web...I keep thinking that this is indeed a 6 x 4 chassis not 4 x 2.
Compare the photo with Leyland Armoured Tender, and also note the AEC Cockatrice Heavy by the way!
http://www.warlinks.com/equipment/ve.../armoured.html