What are the rules governing speed cameras? 
  I am thinking here about warning signs on roads where speed cameras are sited.
 Anyone got any thoughts on this matter?
 May have been caught doing 85 mph by a Trevelo just south of jkt 5 on the M25 - if that's what it's called.
 The one with 2 or 3 white strips just in front of the box that photographs the front of the car.
 
 Cheers
 
 Tim