Irthlingborough Bridge is at 05:18 in this video.
https://www.youtube.com/watch?v=b4DOBjLsz58
I don't think wires will go under that, especially on the slow line.
To build a new bridge over that they would probably have to build a temporary bridge to the side before demolishing and rebuilding the current one.
I was looking Irthlingborough Road bridge (B571) at this before the Pause - it's not one i am looking at currently. As i recall there are a number of options (due to the road alignment) but they all see the bridge being demolished. Finedon Road also gets replaced as does Bush Bridge to the North of Wellingbourgh Station. The bridge i was looking at carries the B571 (Westcoaster is correct with the google maps pin in the post below)
There is a bridge north of Bedford which is a farm road access which has walls so low you can sit on them. I don't know if wires will go underneath, but certainly walls so low you can sit on them I am sure it will be rebuilt as electric wires that close that are unobstructed breaks all sorts of regulations.
I am surprised its as it is now.
Same video shown at 08:05 (look in bottom left corner). Bridge is located near Pavenham.