I was stopped by traffic police who spotted my passenger open his door for a few seconds while the vehicle was moving and the officer gave me a FPN (3 points and £60) for dangerous carriage of a passenger. My partner asked (politely!) for an explanation of the charge and he threatened both of us with arrest for breach of the peace due to the distress caused to the police officers passengers who thought that there was a child unsecured and moving around in the back of the car. We believe that they mistook the movement of our dog (secured in the boot but still able to move about within that area) for a child and was unwilling to back down when it turned out this wasn't the case. I've googled the charge and the only references I can find are to people being stopped for having children unsecured in cars which seems to back this up. I definitely plan to make a complaint about the police officer's behaviour but the question is should I just pay the fine & take the points or would I have a reasonable case if it went to court? The door was open a crack for a few seconds but it was opened by my adult, seatbelt-wearing passenger, we were travelling within the speed limit and both myself and the dog were safely secured also. Thoughts?