To secure a conviction for theft of a motor vehicle, the CPS have to prove (beyond reasonable doubt) that the offender intended to permanently deprive the owner of his vehicle. There's absolutely no chance of a conviction for theft so the charge will be 'taking without consent'.
You could try bringing pressure upon the insurance company to pay up (possibly by involving the local media) but, realistically, I doubt that you'll get anything out of them.
Your only real option is probably to demand the money from the guy who crashed your car. You need to send him a formal letter (either delivered by hand or sent by recorded delivery) demanding the money within a reasonable period of time (say 28 days) and warning him that, if you do not receive the money, you will initiate action through the County Court. If you do not receive the money, you should follow the advice given here:
http://www.hmcourts-service.gov.uk/infoabout/c laims/index.htm
If the guy's got some money (or some property or valuable items which can be converted into cash), you should be able to get something out of him. However, if he's unemployed and living in a rented bedsit with no luxury items, it wouldn't be worth the effort (and expense) of taking court action.
Of course, it's possible that the magistrate's court (or Crown court) which deals with the criminal aspects of this matter could make a compensation order against the offender but I can't ever recall hearing of one being made for such a large amount of money.
Chris