I don't think your gun is a Liverpool W Richards gun as they never traded from a London address. Nigel Brown lists a few Richards in London and a couple have the initial W but none late enough for your proof marks by about 40 years.
That is not to say that Nigel's book is definitive: there may have been a W Richards in London who was gone too quickly to leave a foot print other than this gun.
I would look at the quality of the gunmaking and ignore the name.