Every morning on my commute I would encounter a Numax van that would habitually exceed the speed limit, tailgate other cars, cut in and out of the bus\cycle lane despite the presence of cyclists, stop in the ASL section at lights, etc. Same driver every day. The last straw came when he passed me 20 yards from my place of work going up a hill around a blind left corner after I had indicated that I was about to turn right halfway up the hill into a side road. If I'd actually moved across to the right 2 seconds earlier, he'd have hit me hard as he accelerated up the hill and for the overtake. As it was he almost took my outstretched arm off.
i got the details from the web of the company's local regional sales director and customer service manager and wrote them both an anonymous email letter as well as sending one via their online customer service feedback form. I detailed the previous behaviour of the driver, specifically stating the exact route he took which co-incided with my commute and covered about 4 miles worth that i'd seen him along, and then the final incident. I also gave them a description of the driver and two of the registration plates of the company vans I'd seen him in. I said that it was a friendly warning for them to have a word with the driver otherwise i'd be submitting my video evidence (i didn't have any) and a formal statement to the police.
i then avoided that route for a week, i had holiday so it worked out well. back on the usual route, i've never seen a Numax van since and that was about two months ago.