Apologies for not adding a reply immediately. Been a bit busy.
But I also know that:
a) he was able to drive before being called up (he started working at 14 and had to learn to drive the firm's van), and:
b) he worked in a Q store when he was stationed in Germany (he was stationed at both Iserlohn or Bielefeld). Did the RASC handle Q stores?
So perhaps he was a RAMC person attached to a RASC company as a driver and Medical Orderly. When I was a child, my father often spoke to me about working in the Q store, he said he really enjoyed it, and worked with a really great Quartermaster Sergeant whom he called 'Q Way' (No idea about the correct spelling - it could have been Wey, Whey, or Way). I just assumed it was the Q store for a British Military Hospital, but maybe he was working in a Q store because he was attached to an RASC unit. I don't know. I suppose I will find out when I get hold of his service records.
But his abilty to drive, and the fact that he worked in a quartermaster's store certainly open the possibility tha he was attached to the RASC for at least some of his time in the Army.
Thanks again to Uyraell, Rising Sun and Amrit for all this help. I am really grateful. I will add any (relevant) details I discover when I get hold of my dad's service records. Thanks!