Read what I linked in.
Quoted from Jim Watson:
"Greener describes the practice of Belgian gunmakers sending guns to Birmingham to be prooved so as to avoid foreign markings. They would apply any brand name specified by the seller. The fine old Manton family was likely out of business by the time this gun was made."
Apparently it wasn't uncommon for the lesser British arms houses to contract for firearms from Belgium and France.
They would be shipped, unfinished and unproofed, to Britain, where they would be finished and then proofed with the FAR more desirable British proof marks.
Apparently perfectly legal, although a bit deceptive.
The same sort of thing was done in the United States in which the big jobber Crescent Arms made low cost shotguns that were then stamped with a name very similar to a much better quality British or even American maker.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.