Very simple. If he knew who caused the damage, then that person and their insurance would have paid for it. His premiums wouldn't go up by a bit. But if you got hit by a drunk driver, and they disappeared, then you are using your own insurance to fix your car - so of course your premiums will go up. That's exactly why, if someone damages your car while you are driving it(breaks off the mirror, scratches the side, breaks the fender), at least try to write down the registration number of the other car if you can. Otherwise the damages will be coming out of your insurance, not theirs :P