Hi everyone, thank you so much for your replies!
KGarrad - I totally forgot about the documents being destroyed. I'm hoping this isn't the case but it's something to bear in mind.
philipsearching - my dad's great grandfathers were: AG Harris, John Redman, James Ashford and Thomas Thyer.
MaxD - such great information! Are those dates accurate for the medal or just general?
I should have included a bit more background in my original post, my apologies.
My father is Robert Frederick Ashford and his mother was Joyce Lilian Redman. Her father was Frank Redman who was married to Lily May Harris. AG Harris was Lily May's father.
The 1911 census shows 'Lillie Harris' being 7 years old and her parents as George and Emily Harris, ages 31 and 30. I believe this census to be true as it places George's birthplace as Bishop Sutton which is where a lot of my father's family come from. The 1881 census lists an 'Alfred G Harris' as being 2 and born in Bishop Sutton with his parents being William and Mary.
If I were to guess, I would say AG Harris is both George Harris and Alfred G Harris. The only issue is the dates from the census are a bit out.
My goal is the find out what AG Harris did during the war, but if his record was destroyed then that seems unlikely. MaxD gave some great information, I was just wondering if it was exact, so AG Harris went overseas on 6 Jun 1915 and AG Harris was discharged normally on 30 Jan 1919.
Thank you for all the help everyone