I think you have a case of reporting him to the police. Yes, you didn't have any physical contact with him but it was close enough to have put you in a dangerous situation. I'd do it and see what happens. He might get a few point off his licenses, he might get some fine but he might not get anything. And if he turns out doesn't have any insurance or mot or whatnot then it shall be interesting.
I think you have a case of reporting him to the police. Yes, you didn't have any physical contact with him but it was close enough to have put you in a dangerous situation. I'd do it and see what happens. He might get a few point off his licenses, he might get some fine but he might not get anything. And if he turns out doesn't have any insurance or mot or whatnot then it shall be interesting.