If you buy goods, for example, clothes or shoes, you are within your rights to return the items if they are not:
You should check goods as soon as possible to make sure that they were faulty at the time of purchase. If you want to return faulty goods, you actually have six years to do this in, and if you return faulty goods in the first six months, the onus is on the retailer to provide proof that the goods were not faulty when you bought them, but if you return the goods after 6 months, the onus is on you to prove that the goods were fault when you bought them.
Having said that, goods are only expected to last a 'reasonable amount of time' so if you buy a pair of shoes for £10 and they break after 5 months, it is probably unreasonable to ask for a refund. However, if you buy a £300 coffee machine and that breaks after 5 months, it would be more reasonable to ask for a refund or replacement.
When returning items it is always useful to have the receipts as well as any original labeling and packaging.
If you are returning a faulty item, you need to return it to the retailer, not the manufacturer. Some retailers may tell you that you need to contact the manufacturer but as you bought the good from the retailer, they have the responsibility to refund or replace the item.
If you buy items that are not faulty but you want to return them anyway, for example, because they don't fit, or you don't like the item, then the retailer does not have to offer you a refund or replacement. Having said that, if you return the item in it's original condition, with and labels or packaging still attached, most retailers will give you a refund.