Thanks all. "Where are you actually going with this?" I honestly don't know! I was really cross because I always drive at the set limit - cruise control and SatNav information. I guess this time I got it wrong and, okay, I'm bang to rights and I'll take the hit. What's really upset me is that people drive at dangerous speeds on the roads around our house. I wrote to the council asking about traffic-calming measures. They said 'no - try TfL' (Transport for London), who said 'no - try the Police', who said 'try the Council'. So idiots continue to scream through built-up areas at 50, 60 mph, but I'm caught doing 50 on a motorway...

Thanks. But what distance have they used? Or is it just to back up the radar scan: "Here are two photos X seconds apart showing the vehicle has travelled"?

I've just received a NIP for doing 50 on the M25, allegedly in a temporary 40 zone. It took 8 days for the NIP to come through and my DashCam has already overwritten the relevant videos so I can't check the circumstances. I've got these photos. Can anyone tell me what the yellow lines mean? They appear to show the position of the car at two different times, but what will that show? Does anyone know how to interpret the blurb at the top? What does 'Interval' refer to? Many thanks!