One of the problems with picking out insignia of the war time Civil Defence Service is that the post-war Civil Defence Corps (CDC) had some very similar badges. The key issue is determining the age of a badge is the colour. WW2-period badges are embroidered with 'old gold' whilst the CDC is a rich yellow. The below photo is a good example of the difference.
News about interesting insignia, ARP related info and period photos that turn up.