You're correct in stating that your rights are with the retailer, not the manufacturer.
Your right to a refund (rather than to a repair or replacement) only lasts until the point when you've legally 'accepted' the goods. This period isn't defined in law but, for something like a camera, it might normally only be a few days. (i.e. long enough to get the camera home and to check that everything seems to be in order).
Thereafter, the retailer is obliged to repair or replace the item for 6 years after purchase, if a defect occurs which is due to an inherent fault. (i.e. something which was actually wrong with the item at the time of purchase, such as poor quality components or workmanship). For the first 6 months after purchase, there's an automatic assumption (unless there is clear evidence to the contrary) that any defect is due to an inherent fault. (Thereafter, the purchaser has to show, based upon the balance of probabilities, that an inherent fault is the most likely cause of the defect).
Many retailers choose to define the 'pre-acceptance period' as 30 days because it lays down clear guidelines for their staff and, in most cases, is far longer than the few days that the law would normally require. (So the retailer can truthfully say that 'your statutory rights are not affected').
However, the fact that a member of staff has agreed that the fault has been present since purchase would seem to be an admission that you were never in a position to 'accept' the goods as meeting the required standard. If so, irrespective of the time which has elapsed, your right to a refund remains in place.
Chris