I'm using a SmartWitness (www.smartwitness.co.uk). Because it uses GPS to pinpoint the location of the crash, its recordings are evidential. Halfords now sell a range of dashcams, and there are links to other suppliers here: www.honestjohn.co.uk/useful-websites/parts-accesso.../

There are some warnings about fitting them. They cannot legally be within the swept area of the wipers (which makes them useless in the rain) unless in an area already obscured by the rear view mirror or sun visors. And they cannot emit any light.