I travel on M25 everyday and it's never been great, especially around Heathrow(J16). A few weeks back they started to do some work between J16 & J17, but I've never paid any attention to it until this morning when I saw several pillars for those average speed cameras.
Anyway, I've searched the internet today only to find out, that they are doing widening between J16 & J19 - for following 58weeks. I'm scared to even think what it will do with, already bad, traffic.
Link in the first post