Yes almost has the look of a Shotgun to Rifle conversion when I first saw it ?I know that some higher end guns sidelocks were built by the firm, but all that I have handled were basic boxlocks or hammer guns. The majority were built prior to WWII. I believe production ended not long after the war. It is interesting to see a double rifle. It seems to follow the utilitarian design of the shotguns I have handled.
Which Greener system? A clear close-up of the action and the barrel flats would tell us what you have. Could be a Greener clone, but is more likely an Anson & Deeley. The non-hammer guns I have seen were A&D. A&D by the way is a very strong action and the basis of most English boxlock double rifles.The lock is Greener system.