The Operator swivels round to the opposite direction, and uses a 2nd camera to take a Photo of the rear of your bike/registration plate, to accompany the footage of you speeding towards the Van. They are even known to jump out of the van and stand alongside it, to get that 2nd photo, after you've passed.
I thought I got caught like this about six months ago, going past a van... however I've received nothing (either lucky, or he was pre-occupied doing something else at the time I went past!).