There are two similar (but not identical) revolvers, the Enfield No.2 and the Webley Mk IV, both in .38/200, aka .38 S&W. In this area, the Webley seems to be more available than the Enfield. Both were used by the British in WWII, the Enfield being the standard revolver, the Webley a substitute standard. Generally prices run $400 or so. The Webley Mk VI is in .455 caliber, is a much larger gun and more costly. Many were converted to use .45 ACP with moon clips, but I don't recommend those unless you can handload as standard .45 ACP runs higher pressure than the gun was made for and they have been known to blow up with the hotter .45 ACP cartridge.
Older Webley .455 military models (Mk I-V) should not be fired except with black powder or very light loads.
Jim