Originally, H&H did not make their guns, W&C Scott of Birmingham made them. I believe that Nigel Brown and Donald Dallas commented that London gun makers originated from around the Tower of London area where the royal armouries were. The concept of the London Best gun began with the Mantons where other makers like Purdey and Boss worked.
Certainly there was a tremendous rivalry between London and Birmingham in gun making. IMHO, London being the seat of power and the wealth that goes with power in a kingdom got most of the fame.