Semi-related question - is the Northampton service that runs fast to Leighton Buzzard scheduled to run at 110mph while using the fast lines?
Yes. It's the xx:13 off Euston, a Birmingham service. Although it should be a 110mph unit in theory, /1's, /2's and /3's all turn up on it. I did the 0813 off Euston on Thursday, that was a 12 car formed of three /1's and it did acheive the full 110mph.
--- old post above --- --- new post below ---
Going back to the original question, expanding slightly for the benefit of the of the OP.
Mark 1 units have blue seats and tables and are passed for 110mph. They were not built that way, they were upgraded a while ago which included new Pantographs and motors and numerous other bits and pieces.
Mark 2's have green seats and no tables and are passed only for 100mph (at the moment, rumours abound of them being made 110mph capable).
Mark 3's have green seats and tables and are passed for 110mph, and have been since new.