38/200 is the same as 38 S&W. The original 38/200 had a 200 gr lead bullet, the same as the police load in 38 S&W, but due to Geneva Convention rules it was changed to a 178 gr jacketed bullet. Short answer you can shoot it in your Police Positive.
The problem is that manufacturers don't really know what they're talking about when they label something .38-200 British instead of .38 S&W. Some of the original military ammo was reportedly loaded to pressures up to 50% higher than the anemic .38 S&W originally intended for small-frame topbreaks. So that should probably not end up in a small-fame PP either.
But post-war loads are all over the map. Some modern manufacturers just stick a 200 grain bullet onto a standard .38 S&W charge and call that .38-200. You just never know.
Personally, to be on the safe side I'd just refrain from firing anything labeled .38-200 from anything other than a British (or WW II US) revolver made for than caliber.