But what did I do Officer?

Was driving home from work in bumper to bumper traffic, when I hear a siren going off. It sounded like a car alarm from one of the many car yards by the side of the road but I noticed it was getting louder even though I was barely moving. Looked into my rear vision mirror just as an unmarked police car pulled up behind me. I'm wondering what I could have done and pulled forward to see what he did, he blasted his horn so I figured he was pulling me over. I'm wondering what I could have done in barely moving traffic and as soon as I see a break I pull into the curbside lane, hoping he just moves past me. But no he followed me over, with dread rising I start to park - still wondering what I could have done when he pulls out from behind me, passes by then comes back into my lane and jumps on the brakes. By this time I'm thinking "What the..?", then he turns a corner turns off his lights and pulls a driveway near other police cars. Leaves me wondering whether his shift was over and he wasn't getting any over time. Scared me silly, I had to pull into a service station to gather what wits I had left and cool off with a drink.

Yesterday a similar thing happened, I was at an intersection when I heard a siren, (proper police siren not a car alarm sound). My lights turned green but I sat there until a police car came screaming through the red light. Just up the road he turned his siren and lights off. He sat in traffic for a moment before changing lanes and heading through the town centre, that's when I realised he was heading for the Police Station.

Tell me if I am wrong, but I was sure that flashing lights, sirens and going through red lights was only supposed to be done only in an emergency. One of my friends was once pulled over for making an illegal u turn at lights, she hadn't noticed the police car until it was too late and he went through the red light to get her. The officer approached her telling her that he was going to book her, she said to him "But you went through a red light". He looked back at the lights and realised what he had done had been much more dangerous to others, said to her "lets forget this happened" before heading back to his car.