That happened to me a few years ago where some one told me a van hit the side of my car.
The witness gave me the make and reg which I took to the nearest police station.
I had to present my car documents and fill out a form. The police then gave me the details of the vans owner so I could contact them. Its best to see if they will agree to get the damage fixed otherwise it means going through your insurance so may not be worthwhile in the long term financially if its just a minor damage.
Vorsprung Durch undertaking, overtaking, weaving about and generally behaving like a muppet on Derby Rd, Liverpool. Audi Estate in that boring grey that looks like the car has been primered and is awaiting the top coat! Stupid noisy exhaust too.
Drives worse than Maldonado