Mobile speed camera?

[falcemob]

I have just been along the Sevenoaks Way in St Pauls Cray and there are a couple of white unmarked vans, one's a Transit and the other is a smaller one, maybe a Fiesta. The Transit had a boom about 4 feet long sticking out of the centre of the roof with a long white rectangular thing (about 3 or 4 feet and about 9 inches square). It looked like it had a camera in the end and was pointing at the flow of traffic. They were setting up at 5.45 am and it all seemed to be up and running when I went past again at 7.15.
Is this a mobile speed detector camera or something more or less sinister?