The police aren't interested, the exact same thing happened to me last year.
I was driving down a one way road, double yellows on either side, and there was a white rusty transit in the middle going now where, I waited 45-60 seconds then beeped, waited another 45-60 and beeped again. I got out to find the guy, amazingly he was sat in the drivers seat on his phone. He saw me then turned away still on his phone, I knocked on his window, he got out of the van said the usual "f**k off I'm on the f**king phone and pushed me backwards, I pushed him backs into his van and shouting went backwards and forwards. There was a worker who saw the whole thing while he was having a break.
I was the closest I've ever been to truly spanking someone but I thought, I have a witness I'll phone the police and rightfully claim that I've been assaulted. Eventually the police turned up, the white van man was all friendly and cracking jokes and the police told me there was nothing that could be done, apparently I was the aggressor, they weren't interested in the witness or my passengers account of what happened.
Lesson learnt, I've lost hope in the police, never used them for anything since, always stand up for yourself it makes you feel a lot better.