thanks for the link!
If I remember correctly, those 1911's in .455 Webley were purchased for issue in the Great War, and were reissued for the second go-round. They were/are rare, as not that many were made in that calibre.
You might want to check out the Blue Book of Gun Values, it's likely to be in there.
The last one of these I saw for sale was 5 years ago. He was asking $2,300. No idea if he got it.
It's your gun but it is valuable enough so that shooting isn't recommended by most collectors. Only takes one round to maybe end up with a crack in it. Most guys don't fire their older 1911's at all FWIW.



























