Ash,
Your legal rights under the Consumer Credit Act 1974
"If you buy something which is not of satisfactory quality or not as described, or not fit for the purpose you bought it for then you can sue the seller for breach of contract".
I would suggest that this statement is more than appropriate in respect of a Pounds70,000 sports car that has a major component failure after only 1,300 miles. It could be argued that your car is not of "satisfactory quality" and that the dealer is in breach of contract. All the more reason to involve your finance company and it is important to keep them on your side by maintaining your payments!
You may well not want to get rid of your car, but it is another angle of attack to keep the pressure on your dealer to reach a satisfactory conclusion.
This is only my amateur opinion, I repair ships for a living I am not lawyer.