Average speed camera through road works, (M1 south yorkshire

[Cooper Green]

After being caught (apparently at 56 mph)no pictures available, in a 50 mph road work max speed limit with multiple average speed cameras a couple of years ago, I now set cruise control at 48 mph on our regular trips from north yorks to Derbyshire to visit number one daughter . At the time of conviction we had speed camera and sat nav speed warnings set on our sat nav and yet we still had multiple heavy and light goods/cars passing us through the 50 mph sections at much higher speeds and we get caught.
After attending a speed awareness course at considerable expense and time off work we still set cruise at 48 mph but still have traffic passing at much greater speeds as witnessed today.

Question is do the average speed cameras use number plate recognition and time vehicles between cameras to assess average speed or can I pass through the camera at 49mph and then accelerate up to 150 mph but slow and pass through the next camera at 49 mph and all is well ? Or are vehicles targeted ? We were driving a TVR Tuscan at the time but HGV's were passing in the middle lane ?

[Cooper Green]

Thanks for the responses, but if prosecution starts at 57 mph then why did my endorsement state 56 mph in a 50 mph area ? and if Sat nav GPS cannot be relied upon as evidence in court due to potential inaccuracy then all we have to go on is the info on the summons through the post with no recourse to actuality. I will admit that at my speed awareness rehabilitation course, most people attending where surprised at being caught, it is no surprise in my experience as motorway driving is not part of the current driving test and therefore everyone driving on the motorway is self taught !
Sour grapes maybe, but I still feel the sting 2 years later and consider myself a considerate driver even though I was driving a sports car at the time, perhaps if I was driving the M&S branded artic in the outside lane at the time I may have been immune from prosection.