Just My Subject m8 !!!
Lol my uncle is the "top dog" of Tayside Police - Dundee, Montrose etc etc. I myself have been abit worried by this is the past so I contacted my uncle.
The mobile vans have a range of almost 2 miles m8 - however they can only process the speed of so many cars at once - its a very low number like 2 - 4. If the road was busy then its abit of a lottery bud. Also some of these mobile vans are not equiped to judge speed, they are sometimes there to check car registration, mot, tax and insurance details - When you are driving down the road, the camera picks up your registration - enters it into the onboard DVLA system and it checks everything off the plate number - if it shows you have no tax etc there is gonna be a nice little brown envelope in the post.
However m8 and im not saying it has happened, say for instance yes the camera has picked you up for speeding - there is no chance it will miss your plate - they take 16 real time images of both car and driver - lol that close they could tell what colour your eyes are !!! Plus they have too cameras, either side to take picture of front and rear of car.
The fine etc wouldnt take long to come in the door m8 and dont worry if you well over 100mph the boys in blue would of gave you a visit same day.
I wish you the best of luck bud, theres my info on those mobile B**TARDS !!
Cheers - Andy