That's how they are able to issue 500 speeding tickets a minute on the M25 (london orbital).

I think you are mixing up motorways Rob. The cameras on the M25 rarely even flash as they are set at well over 90mph when the variable speed limit system is off and people don't speed much when the variable system is on. Also, I was under the impression that the cameras were traditional Gatsos, meaning that they use film rather than a digital system. Until recently I drove the camera stretch of the M25 every day.

edit: the M25 gantry cameras are normal Gatso with film

http://www.ukspeedtraps.co.uk/gatso10.htm

There are also a lot less cameras on the M25 than people think, as only about every eighth gantry has them.

Perhaps you were thinking of the specs system on the M6 ?

Or maybe you were talking about the cameras on long term roadworks on the Heathrow section, but again I think those are normal film based gatsos.

I think the spec system is the only digital based (and hence automatic ticket issuing) speed camera system to be certified for use in the UK, but I could be wrong.