Under the Sale of Goods Act 1979 (as amended), anything you buy from a trader must be:
As described
Satisfactory quality and
Fit for purpose
Under this Act, even if your guarantee has ended, you can still complain for up to six years from the date of purchase.
You are also protected by the Distance Selling Regulations if you buy something over the internet, by mail order or catalogue, digital television, phone or fax. These say that:
You have a cooling-off period of seven working days after agreeing to buy, during which you can cancel and
The seller must give you information before you buy, including a clear description, contact details, cost and payment, delivery arrangements and cancellation rights.
This should also be included in a written confirmation of your order. There are some exclusions, such as perishable goods (flowers, fresh food etc) and newspapers and magazines.