(31 May 2015, 6:15 pm)Dan wrote A question for anyone who can answer it which isn't relevant to the trip at all: with reference to the photograph in the article - is '4000' some sort of prototype model like 4001/02?
If so, if this Metrocar is still at the Stephenson Railway Museum as per the caption of the photo, why wasn't it retained in the fleet?
4000 is a trailer which can be attached to a motor vehicle of some sort. Flickr user "metromadme" has various photos of the prototypes - I recommend that you have a look.