I used to get followed by the police all the time in the see and even more so in the skyline. They would u turn, follow me for 5 mins, I assume do all their checks, and eventually cut away. Happened all the time but they never stopped me
Then once in my BMW, the most inconspicuous car I've had, they did the same and did stop me this time. Same again, u turn but lights on immediately. I was cruising and in traffic on a busy main road
"Routine check" was his explanation