This is a World War 2 civilian helmet. Steel helmets like this were worn by air raid wardens, fire guards, ambulance crews, first aid parties, the fire brigade and the police.
They helped protect people during air raids from flying debris caused by exploding bombs.
Most helmets had white letters painted on the front. . They showed which emergency organisation the person belonged to. Here are a few of the more common ones.
A Ambulance
ARP or W Air Raid Warden
FAP First Aid Party
FG Fire Guard
NFS National Fire Service
P Police
WVS Women’s Voluntary Service
Fascinating fact
Many of the helmets were made by British car makers such as Austin Motors who switched production from cars to helmets after the outbreak of war.