British MKII Steel Helmet from World War II, specifically used by the Air Raid Precautions (ARP) service. 
The "W" stencilled on the front indicates it was worn by an Air Raid Warden. These wardens were part of the Civil Defence and were responsible for reporting bombing damage, coordinating emergency services, and ensuring local "blackout" regulations were followed during the Blitz. 
This helmet is in original condition with original liner & chin strap. Stamped 1939.
Plenty of patina, nice and original