Your right to a refund, in respect of faulty goods, only exists until you've legally 'accepted' the goods. The length of this period isn't defined in law but, in general, it just gives you enough time to check that, at the time of purchase, everything is in working order. With a digital camera, this period might last for a week or so but it's unlikely that it could be successfully argued that you'd not accepted the goods after 3 months.
If a fault subsequently develops (due to an 'inherent fault'), the retailer must remedy the fault, either by repairing the goods or by providing a replacement item. The purchaser can indicate which of these options he prefers but the vendor has the right to reject that option (and substitute the other) on the grounds of 'disproportionate cost'. That effectively gives Currys the right to say that they'll get the camera repaired (at no cost to them) rather than give you a new camera (which would cost them money).
During the first 6 months after purchase, there is an automatic assumption that any problem which develops is due to an inherent fault (e.g. poor quality components or poor manufacturing standards) unless there is clear evidence to the contrary (such as a big dent showing that you'd dropped the camera). Thereafter, up until 6 years from the date of purchase, the same rights exist but it is for the purchaser to show, based upon the balance of probabilities, that the most likely cause of a problem is an inherent fault.
Chris