Don Robinson popped up a few times in a search - this was one of them. Check out his handguns.
http://www.guns4u2.co.uk/index.htm
There were several British gunmakers named Robinson.
I saw a website not too long ago selling a "lunchbox revolver" (I wish I had saved the site). Basically the gun was made by a Colt employee who smuggled parts out and put it together at home.
Anyways, you have a pretty cool gun. Part of the fun is tracing their history.