I would forget about it, theres nothing they can do.
I doubt the police will do anything, just some mug trying to be all commie on your ass.
I'd report him for threatening you and tailing you thinking you were gonna get man raped.
End of the day how can he prove you were speeding, what a CRETIN of the highest proportions.
You would think so but not true. A lot of police forces encourage the reporting of "dangerous or nuisance driving" and some even have special hotline numbers.
If reported and the police think there is sufficient cause and the person is a credible witness they can pay you a visit and issue you with a warning letter which remains in the system for 12 months for yourself driving any car and the car which was seen causing the offence.
If they do go down this route, then if the police sees you or you car driving dangerously or causing a nuisance then they can then seize your car. Not too much of a problem as something like £128 plus £12 per day storage (rates may vary across the country) will get you your car back. It would be a pain in the backside though if you were going to work or somewhere urgently and had your car confiscated.
Police forces do vary and here are a couple of examples. I live in Co durham and kind member of the public reported me for speeding through a village. The next morning I was driving to work (same route every day) and I met a local police car just outside my village which I thought was odd as you never see them round our way at that time of day. He then turned round and follwed me for about 10 miles through 7 villages before hitting the siren/lights and pulling me over.
He explained I had been reported but he had followed me and I had kept to the speed limit in every village but gave me the drive carefully/don't speed lecture.
The other one was my boss last week in North Yorkshire. He had overtaken a woman in a small car (he was in his Mercialago and
may have been speeding

) and she had taken his number plate and reported him. The next day two coppers came and issued him a warning letter under Section 59 (I think).
The point of this law after researching it was to stop boy races especially meeting up and racing around which would then allow the police to issue a warning and then if caught again, they could take the car away immediately and remove the problem for at least then. I suppose if you kept having your car seized every day then it would discourage you from misbehaving. It was not really brought in to deal with "normal" motoring offences.
One last note, if the offence is serious enough and the witness/reporting person is "credible" enough, they can prosecute for dangerous driving. However, I would expect the person would have to be somebody as credible as a judge for example and of course the more witnesses, the better.
Sorry for my long post but I have had to do a lot of research on this recently.