Re: No explanation
First time I came across those was on the M20. I had a Saab at the time that had a dirty EGR that would manifest itself as an engine fault - now speed limited to 50mph.
I was going on the M20 and then the engine light came on. Came to a sign for roadworks and speed cameras - OK. I was driving along, stuck at 50 and all these other vehicles were busy over taking me and I was "where are the speed cameras ? I can't see any", but I did see what could be the TomTom camera / traffic detectors but on the pole it looked like a globe or 3 leaves.
Came home, even going downhill the car still stuck at 50. A few weeks later and I had to go into the office again. The EGR had sorted itself out inbetween these trips into London so I was quite happy going in and then, as I approached the M20 it struck. Once again miles of miles of 50mph being over taken by the local snails and tortoises. More cursing and swearing and still no "speed cameras, just Tom Tom's"
I then decided to look these new "TomTom" cameras up and found they were average speed cameras. No mention of that on the M20 - just "Speed Cameras".
Never have I been so glad of an intermittent issue on a car and wonder how many people were caught speeding as they were unaware (lots by the look of it)