I use to work at Marks and Spencer a while back and they used to sell the stock going out of date that was best before in a staff shop and anything that was going out of date and was a use by product at the end of the night to staff for about 60% off. We used to take all the stuff that wasnt sold back up to the warehouse and it went to a good cause...us! We just used to eat most of it and threw the rest away
I don't think supermarkets want to take the risk of being sued because they have given food away that could be dangerous. This country is getting more and more like America with the sueing culture and it wouldn't suprise me if someone tried sueing a supermarket because they got ill from some free food they were given, it's probably a risk not worth taking.