I know one

I actually know one of these guys. He's third from the right, back row. He is Adolf Hitler, once leader of the German people. This photo is post war, moustache removed. The rest of the chaps (not to be mean) seem like fellows that Dad's Army might have rejected.

Seriously, it's a tremendously intriguing picture. Why do so few have war service ribbons? Mr. spectacles has a sleeve badge that looks like a naval Stores Assistant badge (or of that ilk).

They don't have shoulder titles, officer has one wide rank band?

I don't think it's wartime because of brass buttons in place of khaki. The breast badge is distinctly non-military looking but it reminds one of the observer corps lapel pin.

Bear in mind not every use of battledress was military. Even guests of HM Prisons wore ex-RAF battledress or whatever the pigeons called it.

No, this one is a real mystery and I hope somebody clears it up.