Many thanks for posting those videos "Richieb". Very useful indeed as the last time I went over there was on a railtour in the early 1980s !!!
One thing I found odd was after the DMUs had changed ends on the single line after traversing the eastern end of the flyover. There was a 25 speed board after the set of points. i would have expected the points to be 20 or 25 mph, so what speed would the line be prior to that signal which I think was MV61. Just seemed odd having the speed board after the points.
Also noticed after coming off the viaduct and taking the junction towards Bedford the line becomes single and passes over a rather long single line bridge, with another bridge to the left for the line coming out of Bletchley. Presume EWR will be building a substantial new double track bridge there, but doesn't seem a lot of "wriggle room" without acquiring a lot of land to convert it to a double track formation.
Thanks again for really useful links to videos.