Jack Rowe, the late Birmingham trained gunmaker would tell you in a heart beat (and he was correct) that London gunmakers, such as Hellis did not make any boxlock shotguns. English boxlock shotguns were made in Birmingham by the gun trade. As a matter of fact I have in my possession copies of orders from Charles Hellis & Co. to Arthur Howell & Co., a Birmingham gunmaker in Weaman Street (late 1938) for 40 boxlock shotguns. (see page 55 of Winter 2005 issue of Double Gun Journal)
Hellis did not supply the trade, he bought from the trade.