It looks like 'Franco-BELGIAN Stalin's gun'
proofed in Britain prior to implementation of 'Merchandise Marks Act'. Unless I'm blind there is no 'not English Make' mark.
Better made Belgians sometimes wore Sir Jos Whitworths Fluid Compressed Steel barrels.
PS. Looks like unfinished Belgian gun was sent to Britain for finishing, thus the proof marks. Germans in particular backed by Govt. subsidies tried to flood English Isle with their guns,
so to protect their trade Anglos implemented above mentioned act.
