The way Ive always understood it - no matter what the person in front does, you should be at a safe distance, or travelling at a safe enough speed, to come to a stop - whether the person in front does an emergency stop or not.
I know thats not very fair in this case, and hopefully the CCTV will change things and put things in your favour.
The strongest point you have on your side at the moment is the fact that the other driver didnt stop - thats deffo somet sus right there, and deffo counts in your favour.