The BBC investigation revealed that customers at Sainsbury's and Tesco were being misled about the freshness of produce from the meat and fish counters.
Undercover reporter Audrey Brown applied for a job at Sainsbury's in Didcot after receiving information from a former employee. Brown is seen working on the meat counter where she recognised products being sold the day after their sell-by date without customers' knowledge. Brown was also told by members of staff that it was acceptable to shave the tops of some joints of meat to make them look fresher.
At Tesco, an undercover reporter was told to take some steaks that were past their sell-by date and mince them for sale. It is not illegal to sell food past its sell-by date, but it is store policy at both retailers.
In response to the programme, Sainsbury's said: 'We have identified some instances where our procedures had not been followed correctly at that store and have taken the necessary action to ensure these matters are addressed.'
Tesco said the film was unrepresentative. It added: 'Our customers should not be fooled into thinking that this programme has uncovered systematic failures, or that the public is at risk.'