94713,
10L x 3',
Catalog No. 187-Y,
To date, this is the earliest listed Heavy 10 (10L), note that it was ordered on 12/6/1939 and shipped 2/14/1940 to Alfred Herbert, a major machine tool maker (and dealer/agent?) in Britain. Also note this is a smooth bore headstock, non-segmented bearing surface.
it has no chip tray or extras beyond the standard specification (1 3/8 spindle, QCG, cast base UMD. I'm the second private owner and I think it came to me in the same state that it was when bought at a government auction by the first private owner (Birmingham University Geology Department) in about late 1940s (information from one of the Department's technicians in 1968).  I had the lathe from the Department for its scrap value, provided that I moved it off the premises -- real soon!  Interestingly, a recent posting from another UK member gave his serial number as only about 10 or 20 digits away from mine -- they must have shared the same ship !  There are also some (original?) stamped numbers on a few of the castings. Some more history is given by a heavy cast brass plate on the right hand leg, with three lines reading (in cast letters) "Serial  |  No. 3R |  Air Ministry", and with the stamped number "70" above.