All very well to say legally I am entitled to my money back for a faulty item
AFAIK the Sale of Goods and Supply of Services act entitles you to a refund OR repair OR replacement in kind, vendor's choice.
The onus is on the vendor to resolve the matter "promptly", not "instantly". Determining that a fault actually exists would be part of that process, so I don't think a vendor would be expected to drop everything to investigate your complaint. For the record, in my experience it's more likely to be a problem with your console than a new, unblemished disk.
IMO, a (legally) "prompt" turnaround time for this kind of situation would be days, not minutes. If you returned the game 3 weeks ago and they still hadn't remedied the matter,
then it might be time to talk law.
I am not a lawyer or retailer. Here's the act which covers this kind of dipute: [broken link removed]