Hi again, Shaun,
You've been doing some sterling work on this thread, and no, I'm afraid there are no clues written on the back of the photo. It's been mounted on something that is as brittle as a thin wafer, and the very first thing I managed to do was break off that top righthand corner, just by picking it up and not being ultra careful. For a few moments I thought I was going to be ostracised for ever by my brother's family for being so clumsy, but I immediately came clean about it - e-mailed my sister-in-law - and was forgiven (I think!)
keith
P.S. Presumably whoever in the family gave the precious photo to my sister in law might know something about how it came into the family - might ask about that and see whether that provides any more relevant information