Flying suit 1930 Sidcot.........produced in grey green rubberised material, full length side zip also cuff and ankle zips, large map pocket on left breast, two large fleece lined knee pockets - stores ref.22C/53 or 22C/310-316.
First introduced during WW1 by Sidney Cotton. Fur detachable collar - ref. 22C/52.
The 1940 pattern suit was identical in design but produced in green heavy denim material and the knee pockets were unlined - ref 22C/360-366.
The 1941 pattern was identical to the 1940 Sidcot but with the addition of electrical heating elements - ref 22/C773-779.
The above taken from a reference guide to Flight Equipment of the RAF 1920 - 1945.
There should be a stores ref. label somewhere in your Sidcot warmtoast.