-JdK- Michelle in the UK sent these photos. "Got photos from my paternal grandfather on his Norton with sidecar. Phil R. S. Grose was his name. Apparently, Phil was a motorcyclist and engineer in the army, REME. He was also a gamekeeper for many years. He was born in India in 1911, came to England in the 1920s, and lived in Northamptonshire after WW2."
The motorcycle very likely is a WD16H. The registration is postwar and could be from Northampton. My guess is that it was bought from the army surplus, rebuilt and repainted in the late 40s and used with the sidecar. Hard to be a 100% sure off course, it could be based on a 1930s Norton and it could be the Big 4.