An interesting musing.

Perhaps it would be more accurate and a little more enlightening to compose a list of gun makers who produced a gun in 2012 carrying their own name. Then list them in terms of:

Entirely made in the UK. (Westley Richards for example)
Entirely made outside the UK. (William Powell for example)
Partly made outside the UK and finished in the UK. (William Evans for example)

Of course, some makers would feature in more than one list (Purdey for example).

Just a thought.