Shopdog,
Yes many Birmingham knock-offs as well as Belgian.
Names sometimes spelled Close, but not touching! Mortimer had lots of also -rans...and Manton!
I recall looking at a gun supposedly by a British maker, and it was Horrendous!, and was sure it was a bottom of the barrel Belgian job, I would have bet my life on it, But, when I pulled the barrels it had Birmingham proofs.
Not saying the opening post gun is that bad, merely making the point that lesser and spurious stuff also came out of England.
Edited to say my Bro-in -Law had a Westley Richads I gave him. I should see if my sister can find it for photos... It was the real deal.