[David_Hayward (RIP)]

Jan, that motorcycle has a London County Council civilian registration, dating it seems to late war (GXU started August 1943 and ran in theory to November 1946). Other m/cs that had civilian registrations included the St John Ambulance and Red Cross, and Auxiliary / National Fire Service. I wondered if the number you mentioned was a stock number for the frame?

Note also the Road Fund Licence holder with no visible, so far as I can see, tax disc. It may have been exempt as being on His Majesty's Service under the Defence of the Realm Regulations. Fire, Police and Ambulance vehicles were also 'exempt' (actually as now I think they had to be taxed but had a 'nil' charge) but for different reasons as they were emergency vehicles. Or it was required to be taxed but at the nil rate and removing the disc eliminated any dating of the photo.