Comparing the hammer from "Brit plumber" with the one from "Tatanka" strengthens my suspicion that the revolver has been Bubba'ed or made an outing to the Khyber Pass. That hammer has a finish that makes a wartime Mosin look like a Swisswatch. The curved profile of a genuine hammer just does not exist. Time to look at the rest of the innards.
Tatanka, I fear you need to start looking for a source of Webley spare parts.