I picked this rather interesting post card up on eBay for a few quid. It features a large group consisting of:
1) At the back (probably) members of an ARP First Aid Post or First Aid Party. Most have been trained by the St. John Ambulance Association going by the badge on the right breast pocket. All are wearing the serge battledress apart from a couple of chaps top row who are wearing bluette overalls.
2) A line of nurses, some wearing the distinct St. John emblem on their uniform front and one NA.
3) Ahead of these nurses are five ambulance drivers in their distinct drivers' coats.
4) At the bottom are a row of ARP Nursing Auxiliaries (ARP NA) They have the blue uniform with the red embroidered ARP on the front.
Overall, a very nice mix of personnel detailing core first aid and hospital members.
News about interesting insignia, ARP related info and period photos that turn up.