Thank you James, I now believe he was in Mesopotamia, he was such a story teller as a child, its hard to know what was the truth or what was made up, since posting this and after a long search, I have found that he was in the R G F and the R F A, unfortunately his war record were one of the many that were burnt.
I did put this photo on Ancestry via Facebook, the British War Museum were doing a live session about uniforms, they commented that the Cap, being unusual for the 1WW and called it a Chip Bag Cap which were usually worn in the Flying Corps in WW2
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Thanks again for your interest
Marg