You can claim against the retailer, in respect of a problem caused by an 'inherent fault', for up to 6 years after purchase. (An 'inherent fault' is one which was there at the time of purchase, such as the use of poor quality components, or poor workmanship). During the first 6 months after purchase there's an automatic assumption that (unless there's clear evidence to the contrary) an problem must be due to an inherent fault. Thereafter the purchaser must show that an inherent fault is the most likely cause of the problem.
Some people will tell you that you'd need to get an independent report, from a suitably qualified person, in order to show that the problem with the switch is due to an inherent fault. However simply challenging the retailer to suggest an alternative reason for the problem may well be all that you need to do. (Civil law is based upon the 'balance of probabilities'. If you tell the retailer that you're confident that the most probable cause of the fault is the use of a poor quality component it might prove difficult for the retailer to suggest an alternative cause as being more likely).
Argos will probably try to duck out of their responsibilities but, if you hassle strongly enough, you should be able to get the set repaired or replaced.
Chris
(PS: The foregoing would apply even if there was no guarantee at all. A guarantee is a 'gift', usually from the manufacturer rather than the retailer, and is totally unrelated to your statutory consumer rights).