Has heavily blacked out rear window which should have been a clue. Sitting in the outside lane doing 70 with nothing in the 2 inside lanes. I sat behind him like a good boy for about all of a minute before undertaking him and glaring at him as I went past. It was during the glaring that I realised my huge mistake!. The blue lights went straight on and he pulled me over for a little chat. To be fair he was as good as gold, just bored I think to be behaving so provocatively and actually just gave me a warning, probably because my licence is actually uncharacteristically clean at the moment. Never ever just got a warning when I was on 6 or 9 points!