And all we get in exchange for being so sad is, like the rest of western Europe, approximately a fifth the chance of being murdered as in the US. If you believe being armed prevents crime, the natural difference may be much greater. Don't mix up which came first, the chicken or the egg. The law arises because people think killing people is not quite the thing.
It would be legal to own any of the Purdey knives, but not to carry them in places and activities where they don't have some reasonable use, or to advertise them as suitable for combat.
Many dealers, ranging from ironmongers to mostly provincial "gunmakers" who never made a gun, bought in complete guns from the Birmingham or Belgian trade, and had them engraved with their names. Quality dealers, famous under their own names, rarely did so from Belgium, but my guess is that more of them had a basic Birmingham line than didn't.
My sidelock Gibbs, made around the time the modern shotgun was perfected in the 1890s, has steel barrels made by Webley, for a gun made by Gibbs. My guess is that that meant the tubes, rather than a part-finished assembly. Conversely there was a time, I don't know how long, when nobody but Gibbs made their own Farquharson actions, and everybody else's were bought as unfinished parts from Belgium.
The Colt factory, for example, made all of every Colt, and nothing but Colts. In contrast the Birmingham and Liège trade operated by an immensely complex network of the firm's factory work, subcontractors, outworkers etc. A self-employed tradesman might rent bench space etc. in the factory, and sell anything from all to none of his product to his host. I may have scratched the surface of the complexities which existed. My Webley-made barrels happen to be identified by a serial prefix, but most weren't, and the knowledge may be locked up in dusty ledgers, or gone forever.