I think you are right in that it is the M25 , but at ChorleywoodI reckon that is the M25. Given that you cycled on it in 1982 it must be the last section to be opened, between J25 and J27. The photo must be taken from an overpass of some sort. If it is from a road bridge, I haven't found it yet!
Ahh beaten to it. I was just getting the image too.
Second edit - https://www.google.com/maps/@51.648...4!1sHBhF4zCBuxCAz5Lwe_30lg!2e0!7i16384!8i8192