Thank you so much for your prompt and very detailed reply.
My mother-in-law had passed on much information relating to family history and she had annotated the photograph as "Robert Charles Wainwright's Father" which would have made him Thomas. She had also given me Thomas's (original - parchment) discharge paper which referred to the Egypt medal.
However, Thomas's first son was indeed a George - so this photograph must be of him.
Thanks again, Graham