There was an interesting Birmingham Small Arms helmet on ebay this week described as WW2.
https://www.ebay.co.uk/itm/WW2-Briti...53.m1438.l2649
The wording on the decal seems odd though, in 1953 the company name changed from "BSA Cycles Ltd" to "BSA Motor Cycles Ltd", so if this is genuine it may be post 1949 Industrial Civil Defence Corps?
Rob