This gun was made at a time when the English gun trade was facing serious problems with guns being sold with spurious names.This could well be another example of this nefarious trade. For example I encountered a similar gun of Birmingham origin bearing the name, Nock-London fine Damascus. Obviously made long after the demise of this famous maker.
The name, W.W. Forsythe, suggests to me spurious origin!
See W.W.Greener, The Gun, Page 415 for his comments on this practice.

Roy Hebbes