The 42nd (East Lancashire) Infantry Division was a territorial formation at the start of WW2, & went to France with the BEF in April 1940.
After Dunkirk it was reformed in the UK & was redesignated 42nd armoured Div. in Nov 1941.
It served it's time in the UK until it was disbanded in October 1943.
Although very worn it has the 42nd Div sign to the front, & an Royal Artillery flash to the side.
An armoured Div would normally have Headquaters Div Art, field regs, anti-tank, anti- aircraft, counter mortar batt.
Whats left of the liner is dated 1939 & made by HELMETS Ltd,the smooth khaki green paint on the inside has virtually gone apart from that left on the chin strap lugs. So would date the helmet from 1939-41.