
Hi Lucy,
I don't know a huge amount about the Sale of Goods act regarding perishables, but the BBC Watchdog site has some information on there, I know i have looked to use it before, but for an electrical item. I don't know hoe to do links, so sorry if this doesn't come out well, but the site is www.bbc.co.uk/watchdog
Without knowing the exact problems it's hard to know whether it would apply, but if for example, the food was within 'use by' date and had gone off, the store would be obliged to refund, but I guess only if you could prove you had stored it correctly, e.g in a fridge or freezer. Most of the larger supermarkets will out of goodwill anyway.
Hope that helps a bit.
Claire