A similar thing happened to me in an Asda carpark , i was reversing then i spotted a car in my rear view mirror doing the same , i stopped and beeped my horn but he carried on reversing and HE bumped my car , a woman came over and said she saw what happened and shouted at the guy it was his fault as id stopped . A few heated words between us and i drove off after getting the witnesses phone number and name , A couple of weeks later i got a letter from some insurance company demanding my insurance details ! I went to my local police station and explained all and shown the policeman the letter ,He told me to ignore it which i did and heard nothing more , id tell your neighbour to ask the police for advice before it spirals out of control