Picture shown is definitely a Class 91. There is a panto on top to collect the electricity. Colleague of mine was involved with the MkIV DVTs. They had a lot of ballast in them to bring the weight up and therefore allow them to run on the front at 125 mile/h, as crashworthiness hadn't developed to the point where you could have passengers in the front coach of a train travelling above 100 mile/h.
The Class 91s were certainly retired earlier than the much older Class 37s, but had a much harder life. They have been shooting up and down the East Coast Mainline, accumulating more than 200,000 miles a year without a break, although the idea of them working backwards to haul freight at night didn't take off.