It is a British Enfield revolver, officially the Pistol, Revolver No. 2 Mk I**, made by the Royal Small Arms Factory, Enfield Lock, 1943-1945. They were the standard British service revolver of WWII.
The caliber was designated as the Cartridge, Small Arms, Ball, Revolver, .380 inch, Mk II. We call it the .38 Smith & Wesson and it is available at most sporting goods and gun shops under that name. (Note that the cartridge name is ".38 S&W" no matter what make of gun it is used in.)
Those revolvers are solid guns, and reliable; the rough exterior is the result of wartime shortcuts and does not affect the funtioning of the gun. As you know, the gun can be fired only double action. The earlier guns had hammer spurs but reportedly they snagged on parts of tank interiors and the spur was removed. That is the source of the idea that they were "tanker" guns, but in fact from about 1943 on, the DA only models were in general issue. They have been criticized as low power compared with the U.S. .45 ACP and the German 9mm, but the British never considered a revolver as a fighting weapon, more a symbol of leadership, like a saber or a swagger stick.
The proof marks are British commercial proofs, put on when the gun was sold out of government stores, likely around 1957. The ".767" is the case length of the round, and the "3.5 tons" is the working pressure of the ammunition.
I don't see it in the pics, but the broad arrow British property mark should be on the top strap.
Current retail value is around $650, but that is what a dealer might sell it for, not what he would give you for it. Those guns make good home defense guns as it is difficult or impossible for a child to operate one.
One clarification. The Pistol, Revolver No.2 Mk I went through several changes from the time it was adopted in June of 1932 to its formal discontinuance in the 1950's. It was the Mk I** version that was made from 1943 to 1945.