Found this on AutoTrader site....
If you buy a vehicle from a dealer, you’re covered by the Sale of Goods Act 1979. This means it must be:
• Of satisfactory quality, bearing in mind its age, what it cost and how it was described to you. It should be free from serious defects, other than those you were made aware of
• As described. If the dealer says it's a 2-litre, and it's actually a 1.6-litre, you can reject the car and seek a refund or replacement
• Fit for any reasonable purpose. The car should do all that you reasonably expect of it, including any specifics you state to the dealer. If you need a car for towing and the dealer says a 1-litre supermini will be fine, you can reject the car if it struggles
However, if you pay for the car to be inspected, the dealer is not responsible for any faults the inspection should have found and you should always get a statement on the car's condition from the dealer.
If your car is faulty, you have six months from the date of purchase in which you can reject it. You can demand repair or a replacement, unless it would cause 'disproportionate' or 'significant inconvenience' to the seller.
Examples of this would be if a repair would be as effective as a replacement, or if a price reduction would be more appropriate for minor defects.
Dealers must now prove the vehicle was of satisfactory quality when it was sold. This means you no longer need to seek an independent car inspection.
However, if you believe your car is faulty, you must stop using the car immediately, and contact the dealer directly. You need to follow this up in writing, providing evidence of the problems.