You have rights under the Sale of Goods act...
Tell the Dealer that you are Rejecting the car, as it is not fit for purpose, nor of satisfactory quality...
If you have no joy, there is always the Small Claims court.
However, please read below, it's very good straightforward advice.. Shamelessly pinched from here ... BBC - X-Ray X-Guide - Problems with a used car?
* If you're having problems with a used car that you bought...
If you're having any trouble with your used car, you need to tell the dealer that you are rejecting the vehicle as soon as you can.
The dealer who sold you the car is the one who is primarily responsible for its' quality under the law, not the manufacturer - it is the seller who must sort out any problems.
If there is a manufacturer's warranty on the car, this is extra protection for you - it doesn't replace the dealer's legal responsibility for what they've sold.
If you speak to the dealer on the phone, follow up the conversation as soon as you can with a letter so you have a written record of any correspondence.
If you've bought the car on a credit agreement arranged by the dealer, send the finance company a copy of all correspondence - in most cases they are equally responsible for the car. Get more advice on what to do when you bought the car on credit.
* Stop using the car if you can
If you can, you should stop using the vehicle altogether. This is part of the process of rejecting the vehicle.
If you carry on using it, the law may take it to mean that you have 'accepted' the car.
If you stop using the car, you must tell the dealer that you've done this. The sooner you reject the car, the better your chances of getting a full refund, a replacement vehicle, or a free repair.
You're protected by law
One of the most important laws for consumers is The Sale of Goods Act which says any goods sold must be:
* of satisfactory quality
* fit for purpose, and
* as described
This means the car has to be in the kind of condition you'd expect. With a used car, however, you have to take into account the age and mileage of the car, and the price you paid for it.
However, if the seller pointed out defects before selling you the car, you can't complain about them later.