The key questions are:
a) Did the dealer make any representations/statementsto you about the condition of the car that are false in view of the crash damage? Did he say it had never been in a crash, or that it was in pristine condition? Even if he did, can you prove it? If the answer to these questions is "yes" then you may have a breach of contract claim against the dealer.
b) Under the Sale of Goods Act, it is necessary that the car be of "satisfactory quality". This is not a particulary high threshold (as it takes into account the age/mileage of the car etc). However, if it has major crash damage then that may prove enough.
I'd say you are best using the Citizens Advice Bureau to pursue your case. Most of them usually have a large number of keen young lawyers who are training at large law firms, so you'll be in good hands.
Bear in mind, however. that unless the dealer will negotiate you will have to commence proceedings against him to recover your losses. The claim is for £11K, so it won't fall into the small claims track if you commence proceedings against the dealer you run the risk of paying his costs if you lose (although unless he instructs solicitors these are unlikely to be significant).
Good luck.