When I go from my gf's (Cheltenham) to home (Wigan) and back its m5 + m6 all the way, around 130miles.
For the most part there is average speed cameras with cones (no workers or indeed any sign of work being carried out for the most part) for around 2-3 miles at a time, and as soon as you hit the "End" sign about 100ft later you hit a "Roadworks 2 miles" sign!
This covers a huge section of the journey, I used to be able to do it in around 1h45m with no traffic just sitting back with cruise control on. Now with no traffic it still takes around 2h30m its ridiculous. Only 1 or 2 have any work being carried out on them, the rest are just 50 zones for the hell of it I think. My theory is it's the highways agency's way of saying "We're in charge!" and the government's way of raking in the cash.
Especially in the dark the cameras are damn-near invisible and alot of them dont have a "50mph in 3/4 miles" sign, just a "Roadworks in 2 miles" then "50mph" some time later, with a camera about 5ft after the "50mph" sign so it's ANCHORS AWAAAAAAAY! Because even gentle braking would still see an average speed that you could be penalised for.
Once or twice I swear there were cameras with no main big "50mph" sign before them, no "Camera Not In Use" sign, and later on there are repeator "50" signs... brown trousers time!