MIB does work, I used them about 7 yaers ago when I was hit by an unregistered car. However I had to do ALL of the legwork as even the police were useless. I found out the last registered person to own the vehicle, where it was scrapped after a previous accident, I told the police who then bought the vehicle and hey ho they were the culprits. CPS decided that there was not enough evidence to prosecute to I then took out a case with the MIB.
All in all it took about a year from the accident occurring to getting any money back, they will also take a fee (was £300 then) for instance if they award you £1000 compo then you will only get a cheque for £700. But still, better than claiming on your insurance!
Also have a word in the insurance section if you haven't already!
Good luck!!!