The Beesley self-opening action of 1880, may have been the line in the sand. Soon after this time, the best gun trade centered in London. Greener and Westley's guns were falling out of favor/fashion to the London pattern Sle.
Much is made about the fit and finish of the London made gun - that is until a post like this!
...and then everyone wants to dance around what makes up a London gun.
It's like jazz - just a jam session!