if it weren't for the frame on the grip, that looks very much like a snub nose s&w 10. any chance you got a pic of the other side of that gun?
Your right its the Mod 10 from a mfg date of around 1914 / 1915 by the SN Y40381
Note the grip screw on the front strap of the grip frame.....also, not an old colt, the old Colt Police Positives had a screw up near where the web of your thumb rests on the frame (RH shooter), and the slide release mech slot was different. Also on the frame of your gun, note the flare near where the rear of the cylinder rests, this is a classic SW look. On the Colts that area of the frame is flat, and cylinder release face is flat.
Also although this pic doesnt show the SW with the taper coming off the BBL, Early Smiths had it. This is just the best side by side SW/Colt pic i could find to explain what i wrote above. Smith is on the Left, Colt is on the Right

Yours

Also, note on the SW pic i posted, on the BBL you can see where the cylinder rod rests into a piece off the barrel, Note on your gun you dont have that small piece off the BBL, but you have the groove there from where it was located Directly under where you sight is now, on the underside part of the BBL.....
IIRC the chief special is a 5 shot.
shamus
It is
Edit: IIRC BNP is one of the British Commercial Proof Marks (Birmingham Proof House)
This one is more than likely a Lend Lease SW that was cut down. BNP is most definately Brit Proof Marks. Hundreds of thousands of SWs were sent over seas for both World Wars. Looks like this one may have suffered the same fate as the Enfields you remarked about. Its evident in the removal of the cylinder rod catch removed from the BBL of his gun