Yeah it's a webley with a 22 conversion kit installed.Likely a new cylinder created for the purpose that looks like it was proofed. Interesting little conversion there.
The barrel has threading on the end because it is a sleeve that is inserted into the existing barrel, then threaded to be tightened. If you have the original cylinder, you can swap between 22 rimfire and 455 webley.
These are extremely desireable - especially if you have the original cylinder - because you retain the ability to shoot both original 455 and cheap 22 lr.