Hi,
Regardless of warranty, under the Sale of Goods act (cant remember which year) you have up to 2 years, and up to 6 years in scotland, within which you can return goods for repair or replacement to the shop. They might tell you to use the warranty, however, once you go down the warranty process with the manufacturer, you lose all rights to invoke the sale of goods act. By doing this, the shops are simply trying to avoid dealing with the problems themselves, and passing the buck.
Print out the act and take it into the shop with you, highlighting the necessary clauses, as most shop staff aren't trained to know this legal information.