Thanks Roger: the numbers on yours fit the pattern?
Years ago I found the name of a gent online who worked during WWII for Unicam Instruments Cambridge (he still lived there IIRC) and phoned him him up out of the blue. He couldn't speak to No.32 sights in particular, but did say that the company had done a lot of small lot and specialized jobs "for the Ministry", so I suppose that fits with U.I.C. being given the left-overs and odd & ends to finish up or make serviceable, perhaps after the major manufacturers had retooled their lines for other work?
Tangential, but I'd also wonder why Houghton Butcher, Kodak and Watson were dropped from the production completely and replaced with Kershaw, Cooke, Troughton & Sims and Taylor, Hobson & Co.?
Could be their work was not thought to be up to snuff? The Mk.3 builders were I believe all firms with reputations for high quality output.
Would depend on what you paid.
What you really want is Mk.I No.9992 and considering the condition of the rifle it is very likely that the scope is out there somewhere in a similar condition, perhaps even with the matching bracket.