"Iain" wrote in message
...

Definitely three. It was 15 years ago but I'm pretty sure that each
design was painted/liveried in a different colour: one was green and one
blue, the other might have been either yellow or red. I assume the idea
behind this was for easy identification on the feedback form, eg "I
preferred the green train because ..."

The 1986 Prototype Stock actually consisted of three four-car units, two
from Metro-Cammell (one green, one red) and one from BREL Ltd. at Derby
(blue). They operated on the Jubilee line for a while, in six car
formations, before being withdrawn in August 1989 and stored at Acton (the
BREL train) and Neasden (the Metro-Cammell trains, prior to disposal or
preservation.