Am i at fault if someone reversed in to me?

So this morning after my last exam and last day of school i was leaving the parking lot and pulled up behind a BMW. A few seconds after pulling up behind it, it reversed in to the front left of my car causing damage to my front bumper, left wing panel, bonnet and left headlight.At the scene of the accident we got out and told me 'I reversed in to your car' and thought that he immediately took admission of guilt. He took a while to get his insurance information but he also called the insurance company and told them what happened. When i got home i called the insurance company and explained what happened.Apparently he said it wasn't his fault. So im wondering whose fault the accident will be. I have witness accounts from the shop next to the road that said it was his fault and will tell the insurance company that. I should also hopefully be able to get CCTV footage from my school since it happened right in front of it.This is my first full year of driving and my first car accident. My car took the most of the damage while his car only had his right bumper scratched via /r/cars http://ift.tt/2uoYX0d