In that case, you must report it to the Police. This will help you should your insurance and his insurance start pi55ing you about.
Regardless of how close or far you were from the back of his car, he wilfully and deliberately caused a road traffic accident. Plod don't look kindly on these things.
I hope you took some pictures of the incident and his car? This should demonstrate that he was not slowing down for a junction etc.. and support your contention that he was brake testing you.