I have a Hollis/Leonard double rifle. Leonard is well established as maker of Jeffrey doubles (perhaps not all of them, but a significant number). On the double rifles, Leonard put a 4 digit code on the underside of the barrels. Not sure about the shotguns. My boxlock is straight sided, but a friend's near identical Hollis/Leonard double rifle has the scalloped receiver.

I also have a scan of a page of Jeffrey records showing Hollis as maker of a series of double rifles.