Almost certainly not British. I take it there are no labels on it anywhere? Could you provide a close-up of the zip puller so we can see any markings that may be on the metal tag?
It would appear that a name tag was sewn to the jacket breast at one point which to my mind, along with the press-studs would indicate an American item. It may well be civilian rather than military though.
Looks like a B-3 Jacket but with dyed or replaced shearling. Possibly an experimental B-3?