Hi and thanks to all,
Thanks vertugarde for the early 40s date on the curved pockets and front buttons, that was my feeling but I hoped someone more experienced would weigh in. Yes all three are real pockets, made from the same green wool inside. By feel and weight the button disks could certainly be wood. Thanks too for WWII info - my 'too fancy' comment was only a guess. There is of course no reason to assume this is British, I see plenty of vintage from other countries.
Great blog post Nicole - I read it when you posted it. I'm not sure I have the courage to remove the collar! I'm worried what's underneath may be damaged, and I don't know if I could put it back so skillfully. It does feel and look like a collarless jacket underneath. There is also the issue of the curved front hem, which I couldn't restore to it's original, presumably square, shape, though perhaps that wouldn't matter.
Regarding the skirt being used, I've been reading a British 1940s sewing book full of tips on how to remake clothes into other clothes using the less worn parts, which is why I thought of that. Otherwise it's hard to imagine where they would have got enough material to make the collar.
I will have a think about whether to remove or sell as is. I am curious to see what's underneath! If I sell as is I feel I can say it's probably an early 40s jacket that has had the collar added, been relined, perhaps in the late 40s. The lining, by the way, is entirely handstitched.