With the introduction of the serge battledress in September 1941, the vast majority of Civil Defence personnel were allocated a battledress blouse (for men) or jacket (or women) with an old gold CD breast badge (or ARP Pattern 75) already sewn on. Some preferred to retain their original red oval ARP badge and used this instead.
The Post Office was responsible for all CD badge designs and would send out pattern guides of the badge to manufacturers. However, slight variations in the design would then follow as the new badges were produced. The vast majority follow the standard 'old gold' colour at 2¾" in diameter but shape of letters and especially the King's crown do vary (see photos below). The backing of the badges also varies depending on the manufacturer. The vast majority of badges were embroidered but a printed version is known to have also been made after July 1943.
News about interesting insignia, ARP related info and period photos that turn up.