Adding my thanks for sharing your grandfather's story, India Four Two.
I'm not sure if you've read him, but a fellow named Richard van Emden has written quite a few books on the camaraderie that existed between the Brits and the Germans during the Great War. I very much enjoyed reading his "Meeting the Enemy", lent to me by a family friend and WWII bomber pilot and recommend it to anyone interested in that gentlemanly period of our past.