In RC191, Paul Roberts was asking about a bike in a photo with his great-grandfather. It is a Matchless 8B/2 of approximately 1915. The bowshaped front forks, handlebars with a bracing bar, tool box on top of the tank and gear change lever arrangement are all familiar to me.
Twenty years ago I carried out the restoration of a similar Matchless, but had to sell it a few years go. Mine had a Vickers machine gun on the sidecar chassis and an 8hp JAP V-twin engine. It now resides in Bovington Tank Museum.
I hope this helps to solve the mystery.