Many moons ago I recall watching some survivalist drama on TV and one of the shots had a Traffic Warden sporting an SLR manning a baricade. I have no idea what the programme was but the image has stuck in my head ever since... Considering the breakdown of society during the war it is easy to envisage any uniformed authority having some form of martial responsibility, even if only to keep civilian population areas under control and guard important resource centres from terrorists and para-military/militia types.
Obviously local police forces would need to be armed to undertake these duties and who knows maybe traffic wardens! :-) Miniatures wise I have ordered a small group of British police from Killer B Games from their Geezers range which I intend to replace truncheons with SA80's. I'm not sure how useful this range will prove, I want it to but the sculpting does not look anywhere near as good as the likes of Red Star or TAG. Hopefully they'll look better in the flesh as I would like to use some of their masked raiders for NUM flying pickets.