surely they have police in the UK? sure, you may be able to get him into a cab or whatever, but you are simply enabling him to continue his behaviors towards you. and your poor mom......i'm sure she didn't sign up for this?
he's out of control. not a friend. you have become his target......and until you change YOUR behaviors, he will continue. as long as you stay in constant contact, answer the phone, allow him to come bang on your door, disrupt your life, nothing will change.
i know it's tough.....but it's time. you deserve better. you deserve peace. you may not be worried but as a long time member of SR who has seen a lot of stories of things going wrong, i implore you to stop the madness before the unimaginable happens.