This photo was taken in Kentucky. I recently asked two friends of mine in London who were "British Bobbies" if the uniform is correct and what the number 402 meant.

Here's the reply:
This photo is a mixture of various stages of uniform development.

The helmet came into being in the 1980's and was designed to meet public order issues. It was a lot stronger than the old cork helmets and had a strap that kept the helmet in place, rather than falling off the moment the chaos started.

The tunic is pre WW2 and I think started in place up until the 1950's. he is wearing the whistle chain incorrectly. The little hook which is clipped into the button on the chest pocket should be in the button hole of the second hole down on his tunic, leaving the chain across his chest and into the pocket. The chain is attached to his whistle.

The whistle was the original means by which coppers on the beat would call for assistance before personal radios. In those days, there were so many on the beat, blowing your whistle would have other coppers chasing to your assistance.

The black & white strip material around his left arm is in the wrong place. It was worn on the left cuff and denoted that the officer was on duty. If it had been taken off, then he was no longer on duty.

The Number 402 is his divisional number. Originally, the Met and other police forces were divided into Divisions. For instance, I started life on "T" Division and my divisional number was 456. So my epaulettes had a T and the number 456. That number being unique to me.

On the old uniform the divisional number was shown on the collar only (i believe). It then moved to the epaulettes.