The Civilian Protective Helmet, commonly called the Zuckerman, was created to protect the public and Civil defence workers from falling brickwork and masonry. Primarily utilised by the Fire Guard, the helmet was designed in 1940 and manufacture lasted through to at least February 1940. The current earliest date for circulation are December 1940 (12/40) and the latest date (currently known) is February 1942 (2/42).
If you have dates earlier ot later than that I'd love to see a picture of the stamp.
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