JDS1949, thank you for confirming what I suspected! I have hunted through all of the records I can find on Ancestry and wondered if I was missing something obvious - their search engine is not the most helpful I have encountered.
He lived in Lymington in Hampshire just before and after WW1 and was a salesman and then the district superintendent for the Prudential Assurance Company there. They have told me that they have no records surviving.
He had two children, one born in 1911 (my mother) and a son born in 1914. His wife died in 1915, following complications after the second birth. The children were then brought up by their great aunt - their father's aunt.
Absent voters lists is a good idea, I'd not heard of them before and will try that route.
Neil1821, there are no badges of rank, he was probably a private - or the RAMC equivalent (orderly?).
He had no medical background (insurance salesman!) so it was an odd choice of regiment, unless he was a CO.
The uniform shows the Serpent buckle on the belt, a red cross badge on his arm and a metal RAMC badge on the shoulder. The photo was probably taken just as he joined up.
Thank you both for your interest
David