Suit Herringbone Twill OD No 7, One piece, special by Kay Canvas.

These are the 1943 specification coveralls which was used through most of WW2. The coveralls where issued as work clothing for all branches of service including motor mechanics in the Army and Air force, it was also worn as part of the combat uniform fby the armoured units.
This is the second pattern coveralls made in the correct OD No 7 green cotton fabric. These where introduced in September 1943.

The second pattern had a few changes to the first pattern which included the gas flap (extra flap behind the button closure this is where the "special" in the name refers to).