Your best bet would be model railway civilians in OO scale or 1/76. I would check the catalgues of Bachmann and Dapol. Bachmann definitely do a set of painted British police, and Dapol have unpainted station platform civvies.
There's an old Airfix set of civilians that is very 50s - 60s in appearance.
Beware of HO scale models - these are 1/87 and may not be close to what you want. Noch, Preiser and Faller all sell lots of HO/OO figures, whaever that means - check how big they are in a shop first. There's a big range though, including couples having it away!
Modern or older? Quite a few folks make 20mm civilians for WWII and earlier