You're supposed to contact your insurance company in the event of any incident, regardless of who was at fault. Some people might choose to wait to see if the other party contact their own insurance company. Its up to you.
I was rear ended in a carpark, by an elderly man. It was his fault but he tried to blame me, he wasn't even looking where he was going. I took photos of the 'damage' he claimed to be on his front bumper - it was slightly out of line. There was no damage to my car, and no transfer of paint on either car.He said he wanted £600 for a new bumper. His car was a 10 year old corsa, for which a bumper would have cost £80 delivered from Parts Gateway. How many bumpers did he want!!
I took photos of his car in case he would go and deliberately damage it and blame me. Swapped details. Never heard from him again, I think taking the photos must have scared him off as he knew I wasn't going to be ripped off.
So in the event of any accident, no matter how small, its always best to take photos in case you need evidence for future reference.
If you read the policy docs from any insurance company it will tell you not to accept responsibility, and not to enter into any negotiations, ie: leave it to the insurers to sort out.
As for calling the police after a small incident such as a scratch in a carpark, there's no way they would come as nobody was injured.