The ConfrontationA) Whilst I have no doubt that you had no intention to be aggressive, rude or violent - you describe getting out of your car and walking over to the other motorist in order to challenge him about his accusations of your bad driving. My personal feeling is that this is a bad move, for lots of reasons. As confident as you are in your own abilities, we live in a society whereby you just never know who is carrying a knife or other weapon, and things can turn sour quickly. For example, if after getting out of the car to confront the person, they turned violent, and you put them on their back, the likelihood is you're going to get investigated, even if nothing comes of it, and have an uncomfortable time on bail, not knowing what's going to happen. At that point, you'd wish you'd just written him off as a plonker, and stayed in your car.
B) You mention that, after the first time you got out to confront him, you later got out of your car a little way down the road, and did the same thing - and also on a later date tried to speak to him again. Whist, as I say, I'm sure you had no intentions of doing anything other than talking to him, and whilst I'm sure he was gobby and rude first - he does not know what your motivations are for getting out of your car, and is likely to feel intimidated (even if in reality he asked for it). What this basically does is give him a degree of ammunition, if he were to make a complaint about you. Even if it's not the case, if you are the one getting out of your car, and going up to him, it's likely any witnesses would be more likely to describe you as the aggressor or initiator, especially if it kicked off and became physical.
Essentially I expect the best course of action would have been to stay in your car, write him off as a plonker, and if possible just go a different way, pull over for a bit, and create some distance between the two of you.
Just for the record, I am
in no way criticising or being holier than thou - I have made more than my fair share of mistakes when younger, and would be hypocritical to lecture anyone. Before I joined traffic, I have investigated
so many assaults which have come out of incidents exactly as you describe, which have had devastating consequences for folks jobs and livelihood, and have arisen from really stupid, low level disputes over bad driving.
Unless involved in an accident, and thus need to exchange details, I would always suggest to folk to stay in their cars. It just removes *so* much potential for accusations against them.
The "Copper"Based on the posts here, I'd say the chances of him being a police officer are pretty slim, and he's probably just watched too much road wars

Mark makes a valid point, in that, he was displaying an L plate. It's a requirement of the job to hold a full substantive driving licence, so it doesn't make sense that he'd have a provisional licence and be a copper.
Granted, he may passed a car test after 2001, which means he'd still need L plates on a moped, but, the chances of a car driver electing to use a hairdryer are pretty slim.
The way you describing him as talking to you, doesn't fit with how most police officers would talk to people. I certainly don't have any colleagues who would threaten a member of public to "do them".
In terms of being obliged to show you his warrant card, if he's not putting himself on duty and implementing any police powers, then there is no legislation which states he "has" to show you his warrant card. But equally if he's playing the "I'm a policeman and I'm telling you off" card, I can't think of any reason a genuine copper would refuse to show you upon request.
In relation to your PNC question, if an officer see's something off duty which is outrageous and intends to follow it up, they would not be breaching any rules by conducting a check, and then taking appropriate action or submitting intelligence or such like. The rules with PNC are that checks can be carried out providing they are for a legitimate policing purpose. To check someone's vehicle out with a view to dealing with them for a road traffic offence would not breach any legislation. (Although, in all but the most extreme circumstances, it would be quite sad, coppers have more than enough work to do without creating it!)
Ultimately, as has been said on here before, there are good and bad apples in every walk of life and this includes the police forces. The vast majority of coppers are hard working, fair and decent humans, but there are a few plonkers, some of which I have had the misfortune to meet.
Ultimately, I don't think it matters to you whether he is, or he isn't. You've formed the opinion he's a moron, so I'd just leave it at that

In terms of advice on here about getting him to pull over next time you see him and challenge him / film him, I urge you not to. Ultimately if you did, this would be the forth time you've approached him whilst he's been out on the road, and if he were to make an allegations against you (whether he's a copper of not) this would only serve to strengthen his allegation and weaken yours.
I would honestly just let it drop

;y
This post does, however, raise the question of Dash Cams. I now have a front, and rear dash cam in my BMW. Although it has been rightly pointed out, they could be a double edged sword, I have decided that the benefits outweigh the risks. There are SO many aggressive, incompetent, tailgating drivers out there, that I think in the event of a collision, they'd be worth their weight in gold, if only to protect your insurance premium