There's certainly average speed cameras in the roadworks on the junction from the M25 heading clockwise to Southbound. I was rather grateful to my Roadangel on the weekend!
Appears to be some specs/averaging camera gantrys now going up, very close (app 1/4 mile) before/after the commencement of the M3. Do not appear operative currently, but that section of the A316 is already a 50 with a speed camera very close by!