the dealer is primarily responsible for warranty claims. The same thing applies in the case of the sale of goods act - the retailer is responsible to you for any defect in the vehicle.
New legislation was introduced in 2002 - called the Sale and supply of goods to consumers regulations. Under the terms of this legislation any defect that is discovered in an item within six months of the date of purchase is deemed to have existed at the time of purchase, unless the retailer can prove otherwise.
Essemtially, if a product that was faulty at the time of sale is returned to the retailer you are legally entitled to:-
1. a full refund, if this is within a reasonable time of the sale (“reasonable time” is not defined in law but is often quite short)
2. a reasonable amount of compensation (or “damages”) for up to six years from the date of sale.
This does not mean all goods have to last six years. It is the limit for making a claim in respect of a fault that was present at the time of sale. Alternatively, you can choose:
a repair or replacement.
The retailer can decline either of these if he can show that it is disproportionately costly in comparison with the alternative. However, any remedy must also be completed without significant inconvenience to you. If neither repair nor replacement is realistically possible, you can request a partial or full refund, depending on what is reasonable in the circumstances. It may be the case that a full refund is not the reasonable option because you have enjoyed some benefit from the goods before the problem appeared. This needs to be taken into account before a reasonable partial refund can be assessed.
From all this you will see that the law is both very clear and quite vague. The word 'reasonable' is a legal favourite, and is obvioulsy open to interpretation. In your mother's case the six-month factor is unfortunately no longer applicable, and she will need to rely on the warranty and the Sale of goods act, which states that goods must be 'fit' for the purpose for which they are sold. Your mother's car started developing problems withi six months of purchase, and there is obviously a record of that fact.
My advice is that your mother writes a letter to the supplier, clearly stating that in her opinion the car was 'not fit' under the terms of the Sale of Goods act, and that she wants a replacement vehicle or a full refund. She might as well aim high. I imagine that she will not receive a favourable response from the dealer, who will probably insist that he repairs the vehicle under warranty. If she decides to accept this option your mother should insist that she will do so only on the understanding that the car must be returned in perfect working condition, and that she reserves all her rights in law.