In 1941 the Supplementary fire parties who watched over residential area's & the fire watchers who looked over industrial premises were combined to form the fire guard. This was done at the same time as the NFS was created to amalgamate the local brigades & volunteers of the AFS.
The helmet which is a No.2 C, & factory finished in grey, has an FG to the front, the shell is dated 1940 as is the liner. The khaki cotton on the inside of the liner has an ink stamp which you only seem to see on BMB made liners, probably a a quality control stamp.
The chin strap also an ink stamp, that of an M for magnetic, only to be used on civilian helmets.