The Association of Chief Police Officers. This body is a "steering committee" of senior police officers that produces guidelines on how each Constabulary should operate. However, ultimately it's down to the individual Chief Constable of each Constabulary to set his own procedures, and that's why there is substantial regional variation in police procedures across the U.K. For your information, we have an extract from their guidelines on the use of time and distance measuring equipment and this link will take you to the latest version of the ACPO Traffic Enforcement Guidelines in PDF format (1.56 MB).