This jacket may well have been assembled on a USAAF station in England. It looks as if someone used USAAF flying trousers to construct the body of the jacket. The crudely hand sewn main zip is a pre-War Dot and Conmars have been used to close the pockets.The collar strap may be off a pair of A1 trousers.
http://www.ebay.co.uk/itm/WW2-RAF-IRVIN ... 3a6d4552a3
http://www.ebay.co.uk/itm/WW2-RAF-IRVIN ... 3a6d4552a3