Report it to the police as somebody driving away from an accident ( alebeit only small) report it to you insurance company. Make sure both police and insurance company have the car reg.
Police will have to investigate. You will have to produce all your documents and give a statement. Police will have to give you an accident number.
Don't do it till your absolutely sure- a car hit my husbands parked car (with me and my daughter in it) a couple of years ago. The driver didn't even stop to see if any damage was done or that we were ok- I was so furious about it that even though there was no damage I reported it to the police (I had the full reg and make, model and colour of the car.....the police confirmed that he had been reported before, and said they had cautioned him for leaving the scene if an accident etc......all good you would think???
Not so, a few weeks later my husband received a massive hike in his car insurance due to the 'accident' we were involved in!
No-one had been injured, and the car hadn't been damaged but due to my pig-headedness we all suffered, it took nearly a year to get them to drop the insurance hike.....I'm guessing the police told the insurance company, and also passed (SOLD) our details to injury claim solicitors who continually phoned and text us for months after!!!
Be very sure you want to go down this route before you open a whole can of worms for nothing!