In some notes from a visit to Ruislip depot at the end of 1990 I have
recorded withdrawn vehicles numbered 1, 6, 8, 9, 10 and 11 present. This is
the number series that was later used by the Schoma fleet (from 1996) and
previously by the Metro-Vick electric locomotives. After trawling the web at
length I've been unable to trace what these vehicles could possibly have
been at that time - I can't find any references in Wikipedia that cover that
number series. Likewise there's nothing in Brian Hardy's LU Rolling Stock
book.

All suggestions appreciated, even if it involves me searching further!