Thats my main problem the car was not sold as an Approved SEAT it was sold as a private sale through the SEAT dealership , something I didnt relise at the time.
Gas
I believe this would fall into the category of the goods being 'misrepresented ' to you. This is illegal under the sales of goods act. If they tell you an item has/does something that gets you to enter into a sale then that is illegal. I had this argument with a furniture shop when I was assured at time of order that it would be 6 weeks max!! This was the only reason I ordered the goods and they had failed to fulfill. The sales man 'misrepresented' the goods/delivery in order to secure my order. Thats what i was told anyway and it worked when i when to them with it.
I also believe you should try this route. I would say the salemen led you to believe it was an approved used car from an approved dealer garage and as such the car was misrepresented to you in order to get you to enter into a sale with them.
I would reject the car based on this and tell both your finance company and the dealership as such!
Hopefully the finance company should go to bat for you as they have a vested interest in your Tri-Party agreement.
Mike