The Auxiliary Fire Service was formed in 1938 to boost fire protection in Britain with the onset of World War 2 in 1939. The service lasted until well after the war finally disbanding in 1968. During its lifetime several variations of cap badge exist, all are fully pressed one piece stars with enamel letters. Several manufacturers also were in production of this cap badge leaving several variations on the common badge. Large & small letter A's, light red & dark red variations & thick or thin letter F's. I have 4 different variations in my collection but i am sure there are more. 
This cap badge is the light red variation with a large A, thick F & on a very flat star. Most AFS badges are slightly domed but this is an uncommon example probably a post war manufacture. It retains both cap fixing lugs to the rear of the star & there is a small chip to the enamel of the letter F.