Salter and Varge, London circa 1920 +? Wholesale arms and ammunition manufacturers,agents and merchants.Sold a wide variety of shot guns
One of their suppliers of shot guns was S. Wright and Sons of Birmingham. [1930 -1970,s] Wright,s were owned by Churchills in the 1970,s . All of Churchill,s box lock guns were made by them at that time. If the 28G; has Birmingham proof marks you may have located avery fine gun.
A 20G Salter and Varge box lock with London address, is currently being offered for sale in the U.K. for 1800 pounds!