Arsehole was driving right up my exhaust-pipe all the way to work, decides to overtake on a narrow street and then slams on the anchors so I go into the back of him.
No major damage but insurance company likely to blame me. Plenty of witnesses but none who were able to stop, so looks like it’ll be my premiums that are hit. I’ve disputed the fault claim with my insurers but as it’s my word against his I can’t see much scope for success.
I’m fine (and so is the other driver, although what’s the betting a “stiff neck” will appear soon) and fortunately my daughter wasn’t in the car with me. In the grand scheme of things it’s not a major drama but what a crappy way to start the day. 
VENT VENT VENT VENT VENT!
This sounds like a road rage incident. The other driver tailgated and then pulled in front and stopped. Maybe you should have pursued it on that basis at the time. Any chance you were driving slowly and blocking?
Bummer! Most states are going to have a statute defining and outlawing “Following Too Closely” and will have some jury instruction essentially saying you’re liable if you rear-end someone else. However, both conditions can be overcome if you can demonstrate careless/reckless behavior on the part of the other driver was the real cause of the accident.
That’s tricky to do with no witnesses. But if you’re certain the other guy got in front of you and then locked 'em up for no good reason, make this your story NOW and stick to your guns. Also, what is the stand-alone evidence: How many lanes was your piece of road? Which were you in? Does the location of the damage to your front bumper and his rear support his moving into your lane (your left front/his right rear)? When did you notice him making his maneuver? Was it clearly hazardous? What did you do in response? How long had he been in front of you before his brakes were on? Was traffic heavy–could he have been responding to traffic ahead of him?
But yeah, if he was just some douche who stole your gap in heavy traffic you might be screwed.