Looks like your onto a winner mate, at the end of the day the copper just wanted to be a prick but couldnt do you for anything There is NO WAY he can make you change your exhaust UNLESS it is found to be illegal for whatever reason and then you have a little pink ticket in which you have to get the problem sorted within 2 weeks and get a MOT station to check it I was being followed by a highway cop before, had buckets with harnesses, I pulled into the petrol station and started filling my car completely ignoring the cop until he comes upto me and says, " come have a chat with me once you have finished" So I drive to where hes parked and he asked me why I didnt have a seatbelt on and I said I was wearing my harnesses, he came and had a look then walked round the car checking all tyres etc came back and said, you sure you was wearing them? I said yes and he replied well your exhausts are too loud so on your way I was like up yours