A couple of years back, I was driving on the inside lane of the dual carriageway at about 70. An Impreza on the outside lane was behind me and gradually closed up the distance until he was in my blind spot. Then he just stayed there, in that really annoying spot where you think to yourself, "Either overtake me or pull in." Anyway, he did neither, and I was about to floor it when he put on the blues and took off, presumably after another car!
That was when I first realised that: (A) cops can drive unmarked Imprezas, and (B) they employ dodgy baiting tactics.