Peter fitted some up to scopes he overhauled around that time if people wanted them. Could be one of them.
This is the last pair, the gent who made them was a very skilled self-taught machinist, but he passed on years ago sadly.
Did a bit of experimentation at the time on how to rectify the problem of detent plunger holes worn ovoid and the backlash that develops as a result. Peter illustrates his solution in his book: detent plungers made to the No32 Mk3 pattern, but larger to fit the Mk.I/II scope plunger holes.