I recall someone who attended the Wales weekend but chose to do their own drive only to get caught by a mobile (in a well known 30mph location), whereas all the others on the official drive got safely through a little later on
I'm sure that member's name will come back to me..................
That said, the siting in that case and like many mobiles whether that be vans or hand-helds are often in locations where it is all too easy to transgress but there is no particular hazard. But we can all call to mind hundreds of locations where even 20mph in a 30 area can be hazardous but how many times do you see mobiles operating there?