We've learned a lot since that thread Kathy.
According to W.W. Greener, William Fullerd was the last to make barrels in London and supplied all the "best" makers of that era until 1844. Lancaster supplied Purdey (and others) in the early days before he became a gunmaker himself.
The first Purdey Pair Nos. 10614 & 10615 were delivered January 1, 1880 with the “New Whitworth Fluid Pressed Steel.” Lefever Arms Co. was the first U.S. maker to supply Whitworth steel for their Optimus in 1887.
c. 1890 James Purdey II wrote concerning steel barrels that he preferred damascus but acknowledged that "...weight for weight steel is stronger than iron and shoots harder, though not of so handsome an appearance as damascus barrels." He favored Belgian damascus because "...not that when thorough sound English damascus can be obtained they are not superior, but because Belgian workmen are more careful than English, and there is thus less risk of slag and rubbish getting into the welds."
W.W. Greener, "The Gun and Its Development", 1907
"The figured barrels used by London makers are now imported. In the Midlands the barrel welders are not so numerous as they were, the demand for twisted barrels not being so great as formerly. The very best barrel-makers who manufacture for the London, Berlin, and Vienna markets are to be found at Chaudfontaine or Nessonvaux, both places a few miles from Liege."
