I've been seeking some legal guidance, see below:
BUYING FROM A DEALER
The Sale of Goods Act 1979 (as amended) is the statute which covers the sale whether it be a car, clothes or a toaster that you are buying.
When buying from a dealer, the law says that a car must be:
Of satisfactory quality
As described, and
Fit for the purpose
Satisfactory quality - It must meet the standard that a reasonable person would regard as acceptable and be free from defects, except those which are specifically brought to the attention of the customer.
Fit For the Purpose - It must be reasonably fit for any normal purpose and this includes any purpose that you specify to the seller.
If any of the above are breached then, in theory, you may have the right to reject the vehicle and get your money back if you are reasonably quick. Alternatively the dealer might offer to replace or repair the car.
Once you have informed the dealer that you wish to reject the car, you must cease to use the vehicle. If the dealer, or finance company (if bought on hire purchase), is disputing the rejection, then it's up to you to prove your case. You will need to pay for an independent assessment of the car and sue for damages. If you do choose a repair, insist the dealer provides you with a hire car or pays any travelling expenses you incur while your new car is in the garage.
If the car is new, it is likely that the claim will be too high to be fought using the Small Claims procedure so you may have to pay for legal representation. All this can be pretty daunting and expensive. You need to weigh up the pros and cons before rejecting a car. Would a repair do just as well? Selecting a dealer that offers a no quibbles exchange policy may help.
When choosing a dealer, find a well established firm with a good reputation

. Check if the company belongs to a reputable trade association that operates according to a code of practice supported by the Office of Fair Trading

.
EXAMPLE CASE
I want to send back my new car and get my money back.
Q -
I picked up my new car on 31 October, however, it started stalling. I returned it to the dealer 2 days later and was advised there was a manufacturers fault. They have given me no definite date for repair and it has been in the garage for over two weeks now. I paid £6,000 cash and have £2,495 on credit. They have provided me with a hire car but I want to cancel the car and have my money back. Am I legally entitled to do so?
C.D, London
A -
Your letter indicates that the dealer is in breach of contract because your car is not of satisfactory quality (section 14 of the Sale of Goods Act). This is assuming that the problem was not revealed when you took the car for a test drive before you bought it.
As a consumer you are entitled first and foremost to have the car repaired within a reasonable time and without significant inconvenience to you. As the garage has supplied you with a hire car, arguably, the offer of repair is not causing you significant inconvenience.
If, however, the delay in getting the repairwork done persists, ask for a replacement car. If the garage has not got one then you would be entitled to an appropriate price reduction. The right to reject comes at the bottom of the pecking order of remedies available to a consumer.