A head warden with a 1" black band over the top of a white painted helmet, this paint scheme would date from October 1941. Before this it would have been a white helmet with a black diamond, or a 2" wide black band. To complicate things a bit, London markings would be white helmet with 1" black band meant a post warden.
Due to thickness of paint date not visible on the shell but the liner is dated 1939, & made by HELMETS Ltd, the size is a 7 3/4 which is the largest they made. Which means there are no buffers riveted to the liner.