Mk2 Factory Civil Defence

Pretty sure these helmets were used by factory workers or the people who worked in factories who were part of the civil defence to protect the workers & premises. Of very basic design, no chin strap lugs, no Mk2 liner, no nut & bolt,& the rim just folded over in a Dutch bend. It just had 2 pieces of rubber sorbo & a leather riveted to the shell chin strap.They always seem to be painted grey & have no markings.