Thank you everyone for the input. I have a theory about who this might be but it is only that at the moment. The person who I think this could be was a chap named Percy Hayward Squirrell born July 1891. My 2 x great uncle.
If it is him, these are the facts I know relating to his war record...
. He was a driver in Salonika.
. He was RFA (68th brigade). In another document I have for him his regiment is listed as 179th Brigade.
. He enlisted 1915 in Deptford, discharged 1918.
. I believe his regimental number was 431953 (does that sound possible)
As I say, I am far from certain that this is the fellow but from the little I know, he does seem to fit quite well.