Someone has drove into the back of my car?advice needed?

I was driving my car down a cobbled hill when I heard clunking noises. The noises were loud and I was worried so I decided to pull in on the side of the road (on double yellow lines - half on the pathway and half on the road). I was waiting for vehicles to pass before I got out of my vehicle to investigate. The next thing I see is a blue BMW travelling at some speed coming down the hill so I waited,however he drove into the back right handside of my car jolting my whole car forwards. Every other vehicle passed me with no problems and the road was wide enough as both a BMW X5 and a White transit van passed me with no problems. I felt it was the safest place to pull in to check my car.He was very apologetic but also very calm at the same time.Id like to know if because I was on double yellow lines will it be classed as my fault even though he drove into the back of me? He had to reverse back behind my car after hitting it to allow other cars to pass through.I'm gutted as I have one problem with my car and now I have two problems. I don't know what else I could have done to avoid this happening to me. The road was clearly more than wide enough.Please help