Hi Roy
Many thanks for your response, if I was not tired last night I would have remembered to ask if it had English Proof Marks which a Commercial rifle would have

The arming of "Armed Trawlers" is interesting, they would use .303s
There are many on a trawler wreck just off here in Plymouth

I am also interested in the arming of merchant ships in WW1, with older guns from 3 pounders to 4.7 inch
As I diver I have dived on many WW1 wrecks in the English Channel and recovered (legally!) shell cases and small arms ammo.
Most was .303 but often other, 6.5 X 54 Mannlicher and unusually, 44/40 Winchester

Early in WW1 many American shooters gave pistols and rifles to the British War Effort (thanks guys, we were short as usual)
Some of these were given to the IIRC Home Defence Force? predecessors of the WW2 Home Guard
But I believe some were issued to these armed ships as it would save the.303s for more regular units
Ammunition could be sourced from Eley etc.

Anyway, I digress and ramble on...............

Good shooting

Tony