And today the postman brought me:
I don't know if the box was always with the watch - but its not impossible.
Hairline crack at 11; rear cover a bit misshapen, but in pretty sound condition otherwise.
The movement is marked 13 SB - a calibre I can find reference to but no details about. Anyway - its running. Allegedly serviced about a month ago. One of the case screws is way too big but seems to do the job.
The serial number comes out about 1920.
The case is by Dennison and has a Birmingham hallmark for 1922.
The strap was brand new - but way too feminine. One of the wire lugs is a bit bent and won't take thick leather - so this strap was the best I could do for now.
IIRC, radger has something similar.