As much as the police are cocks most the time, i have had 1 or 2 fair ones, (yes they do exist!) i remember we were driving to Weston Super Mud one weekend when my mates tax disc fell off and flew out the window!.
Anyways we got pulled and explained it had flown out the window earlier that day (even to me it sounds like a blaitant lie!) but he said he would let us on our way and if we didnt have a tax disc we would be receiving a letter in the post