Make sure you got reg plate and a good address ie written on a letter etc, otherwise follow them home!
My old man borrowed a car of mine a while back to help my bro move in at uni (I got an 18month old Beemer for a 4 year old Laguna). It was his 60th Birthday and some To55er gave him a present of re-shaping my door by driving into the side whilst speeding from a junction. Police questioned my old man (an ex copper) about running a red light, turned out the other guy was in the outside lane racing to get infront of the guy in the correct lane. The V5 log book said it was a girls car who had sold it! no trace back to Mr W. Anchor.
Sorry for abuse, still get wound up 2 years latter, don't forget we pay their premium with an extra ?30 on your policy!