This is also from the Which site. Used cars are a bit of a mine field and sadly most dealers can afford court and solicitor costs easier than the average buyer
Second hand car from a dealer
When you buy a second hand car from a dealer, you have the right, under the Sale of Goods Act, to expect the car to:
be of satisfactory quality (taking into account its age and mileage)
meet any description given to you when you were buying it ( whether in the advert or in discussions prior to sale)
be fit for the purpose (for example, to get you from A to B safely).
If the second hand car does not meet these requirements, you have a right to claim against the dealer for breach of contract.
If something you buy is not 'as described', or if the seller is guilty of misrepresentation, you are entitled to:
give the second hand car back and get your money back, or
if you want to keep the car, ask for compensation (usually the cost of any repairs it needs)
But, if you buy a second hand car that was not described as being in excellent condition or good working order, and it breaks soon after you buy it, you don't have any right to reject it, or to claim compensation.
When you buy a second hand car from a dealer, you still have statutory rights under the Sale of Goods Act
If you bought your car on credit card, you may be able to claim under Section 75 if things go wrong.
If you claim on your warranty, your legal rights to reject the car still remain.