Thank you all for the info and advice. I didn't take my son's account at face value. A few days after the incident, I visited the scene and met the owner of the house just opposite. He called his 14yr daughter who had seen the whole thing and who confirmed my son's version of events. Her parents didn't want me to involve her as she was recovering from a serious illness which I understood fully. I still don't want to involve her but I suppose if hardy comes to hardy.....