Hi Jim - Wow, you have been busy!! Some of your information I have already discovered but where I have failed you suggest some avenues to try that I hadn't thought of.
However, what I did find was on the form that was filled out when Thomas joined up in 1914. He has declared that he was in the forces before - Royal Garrison Artillery - invalided out 17th May 1906. The RGA were stationed near Gosport in the early 1900's - which is where Alice May Griffiths came from. A possible link?
I agree that it is unlikely that the change of name was registered anywhere but I will try the library regarding the book you mention.
So, I shall plough on and hope to achieve a breakthrough.
Many thanks for your help. Pam