I think i got caught speeding?

I was on my way home from work last saturday, going down quite a steep hill, the limit was 60mph. I must have been doing around 64mph and passed a lay-by with a police car there. However, the police man was sitting inside the car and I couldn't see a gun or anything. I can't remember for sure but I'm pretty sure I slowed down to 60 before passing him though! Anyway, can a policeman use a speed camera gun inside the car?? I'm so paranoid right now, I hardly speed and never tailgate people, damn! xx