I go through there a couple of times a week on my way to Hemel. Did it for the first time today on the 996 and its just about bearable, but the lanes are so narrow now that flitering is a slow old job...
certainly in the peak periods (that'll be 5am to 11pm then!!!!) they cant be catching anyone speeding as its snails pace at best
But, got to say, I dont think they can be catching people on the variable limit section as only 1 vehicle in a 100 can actually be doing what it says above the lane...