Without a photo and some more information about its markings, it's hard to tell you anything.
You possibly have a Webley Mark VI, but it could also be a Webley Mark IV, or an Enfield No. 2, Mark I or Mark I*. All of these were .38 caliber (and will use the .38 S&W cartridge).
(The Webley Mark IV was made from 1892 through maybe 1932; the Webley VI was made from 1913 until maybe 1939, and some were made by Enfield; the Enfield No. 2, Mark I was made from 1936 until maybe 1957; and the Enfield No. 2, Mark I* was made from about 1942 through maybe 1957.)
Price will vary according to the pistol's type and condition. Some Webleys could be worth as much as $1,000.00, and as little as $150.00. The Enfields run from $350.00 to $100.00.
This information comes from The Standard Catalog of Firearms, 2010; and The Standard Catalog of Military Firearms, 5th Edition, 2009.