My tuppence worth now. I think either Railway or Bus/Tram employees!! The cap badge on the rear guy has the outline of either a steam train or a high roof tram. The letters on the right lapels are their positions (DG..Driver/Guard) The ones on their left lapels are actually numbers IS is infact 15, theres also a 37 visible!! Tunics are not military and the buttons close up dont resemble any ive seen. Ive been collecting Military uniforms for years now! Definatly Civilian!!
I think you are right. Here are a couple of photos of their uniform (Port at War book) and buttons (e-bay) showing the resemblance. Also, the DG could mean 'Dock Gate' policeman. Bri