bentleywr:
You have a .38/200 British Service Revolver manufactured in 1940 or 1941 under commercial contract for the British Empire. The .38/200 was the British Service load of the time, a 200 grain lead projectile in a .38 S&W case. This round was also known as .380 Revolver. The P stamping may be a British proof mark. 35329 is an assembly number used to track parts in the factory. It was not recorded and has no meaning after the gun was completed.
The gun is a K frame and aftermarket grips should fit it.
A lot of these had the chambers bored out to accept .38 S&W Special cartridges, its a simple test, if it fits, then its been bored out. Converted guns will bulge and possibly split brass and are only worth around $150 or so. An unmolested BSR in excellent condition should be worth twice that.
Edit: Just saw your pic. Its been refinished, the grips look like they are plastic Franzite grips, S&W did not nickel the hammer and trigger and the BSR was a blued finish gun. If it has been converted to .38 Special I suggest you stick to standard pressure lead loads only.