My "William Evans from Purdey's London" is visually virtually identical to yours. My engraving is as complete as yours, but a slightly different pattern.
Yours, like mine, is a treble screw grip Webley & Scott. Found on the bottom rib is a five digit serial number. I compared this number with the W&S serial numbers, and dated the BARRELS to AD1901.
Can't recall where I found the W&S serial numbers on the WWW.
Hope this helps.