Now, this brings back memory, almost forgotten about this
The only time I ever saw it, it was a pair of Class 20 in Hunslet-Barclay livery, top and tailing the coaches
I was invited onboard the set whilst it was idle for a few hours in Aberdeen
I've had a basic search (so far), but could search later on today
http://www.flickr.com/photos/justindperkins/4432949525/
http://www.flickr.com/photos/chrisboon/4238596386/
This looks like the Eastern region one, operated by Chipman, possibly converted from an EMU
However the one used in Scotland appeared to be green in colour, so may have been the Fisons, but also had several TTA tanks (which carried water)
From memory, Rail Magazine did an article shortly after the Class 20 locos were released in this livery, and included all of the contractors that were to be used