Hi,
If it does not have hallmarks it is not likely British. I am guessing that it is continental European but whether French, German, Belgian, etc. I do not know. One thing I noted in my books about German guns is how uncommon silver decoration seems to be. There are certainly examples with silver side plates but not to the extent you see that practice on French and Belgian guns. Given the motif of birds, rabbits, and hunting dog, I suspect it was from a fowling gun, maybe a French one.
dave