At the end of the day, whether you deal with themself or through a third party (such as the solicitor or, possibly, the employer's vehicle insurers), you've got to sort it out with MIB. They're the only ones who've got the money to pay you some form of compensation. However, the MIB scheme is a voluntary effort by the insurance companies to make sure that you get at least some form of payout when you're injured by an uninsured driver. The funds are limited (because they come from an additional charge on the policies of law-abiding drivers) and the payouts are often far less than you'd have got if the other driver had been insured.
If you've suffered any level of disability through an injury while at work, you should be claiming IIDB:
http://www.direct.gov.uk/en/DisabledPeople/Fin ancialSupport/OtherBenefitsAndSupport/DG_10020 628
That's totally separate to any payout from the MIB and, while it's only a small weekly amount, it would seem foolish not to claim.
Chris