In 1939 it was decided that ARP & home front helmets should be painted black, before this they were painted khaki green.
If you have a number of home front helmets painted black I bet some are inside khaki green, where they changed over to the black.
For some reason this one stayed khaki green, whether by choice or they might have left the ARP taking the helmet with them.
Making this one quite rare & hard to find.
The shell is dated 1939 & made by F&L, but chin strap lugs dated 1938, liner is a HELMETS Ltd made one & dated 1939.