I can't quite make out the serial number from the angle of the photo, but that seems to be a British military contract revolver; if the first three digits are 887, it is from 1941. If the first three digits are 987, it is from early 1942 before April, as that is when the serial number sequence was reset for the second million of this model. The new numbering sequence had a V prefix and guns with that prefix are referred to as Victory models. Since your gun is a wartime contract gun without a V prefix, many would call it a Pre-Victory.
The general model is called the S&W Military & Police or Model of 1905, Fourth change. These were made in great numbers during the 20th century and as a group remain the most successful model S&W ever made. The basic chambering for these was the .38 S&W Special, but the British ordered guns that chambered the .38/200 cartridge, which involved a 200 gr bullet in the shorter .38 S&W case. The two cases are different lengths and slightly different diameters. After the war, many British guns were converted to 38 Special by boring out the charge holes to the length of a .38 Special case; you should check your gun to see if it chambers a .38 Special round. If not, then it is an unmolested .38 S&W revolver. From a collector's point of view, that is good.
There is a big collector's market for WWII S&Ws, partly because so many were made that it is not too expensive to get involved in collecting them. But there are many identified sub-varieties, and guns with uncommon features can achieve high values.
At least one of the proof marks on the gun (up arrow inside a C) is a Canadian mark. BNP stands for Birmingham Nitro Proof. Once released from military duty, decommissioned revolvers had to be proofed under British law before they could be released to the civilian market. That's were most of the markings on your gun come in.
There are Victory specialists on the forum who know way more about these guns than I do, and I suspect you will hear from them shortly. That looks like a pretty nice specimen to me, and I hope it has not been converted to take .38 Special.