A few modifications to Gary's identification:
This is indeed an Enfield No. 2 Mk I**. Based on the Y prefix serial, it was manufactured at the RSAF Enfield in later 1943.
It was not manufactured specifically for the tank regiment. It is correct that the earliest Enfield versions without the hammer spur from the mid-1930s seem to have been delivered to the Royal Tank Regiment.
However, due to a general engineering change in 1938 all Enfield revolvers from then on were produced with the spurless hammer until the end of production after WW II, the Mk I** as a true DA-only gun without the innards for SA. They were produced at Enfield, Albion, and HAC in Australia, a few hundred thousand in all.
So it is incorrect to talk, as you will find occasionally, about a "bobbed hammer", nor is the nomenclature of a "tanker model", also often encountered, correct. The spurless Enfield remained in service with the British as the standard sidearm until the 1960s, although the FN HP was phased in as a replacement beginning in 1957.
The British service cartridge, officially the .380 Mk IIz 178gr (jacketed), is dimensionally identical to the .38 S&W, but many loads are up to 50% higher in pressure. So any .38 S&W load can be fired from an Enfield (or .38 Webley) without concern. The gun can take it.