Have had a very similar thing happen to me, however the officer was: Off duty and not undercover and on his way home ununiformed. He thought it would be exciting to do me for sitting in the right hand lane for too long. I was randomly passing cars, beside the fact noone ever gets done for this, it was 1am and the highway was almost deserted. He wanted to undertake me on the left but a car was there so he go cut off. He waved his hands around and started yellings comments out. He also thought it would be exciting to highbeam me for a while and chase me until he pulled up beside me flashing badges and yelling out comments. Aside from this to help his claim and to add a bit more excitment he decided swearing and making a few general accusations were ok. "I've had a sh*t day at work and I dont need ppl like you making it worse" I just went along with him agreed and told him i'd just dispute it in court. A letter was sent to the police station by my law firm and the cop decided his actions were justified. We informed them we would be taking it to court. It's been 4 months and I havent heard anything back, funny about that.
I'm in no way saying that the police are hopeless and that they're all "out to get us" I know that in many situations I would and will require their help. I'm just saying that some perhaps need to look at what they're doing and make sure their not doing it to satisfy their own need of anger or get back at a stereotyped group (the car group). All in all if it was nanna in her corolla, many of the fines we get simply wouldn't happen. So if you get a fine you think is wrong or unjustified, dispute it.
my 5c (2c is rounded down nyway)
Matt