Hayden,
If you were on the motorway doing 78/79, you should be OK. Most static UK speed camera's are calibrated for 10% + 2mph, the mobile one's are a different kettle of fish and I'm not sure about them. The useless info you get from reading 'bike mag's... ;)
I think the little white boxes are camera's, but they're usually hidden in the back of an unmarked van, generally parked up on the Police car "mounds" on the motorway with one rear door open. Unless of course, they were doing a survey of the road, and the white box was actually a theodolite, but they're usually green-ish.