Asda has been fined £300,000 after dead mice and flies were found at a home delivery depot in north London.
They were discovered in the bread section of the site in Enfield, which distributes food to customers in Essex and London.
Council inspectors also found mouse droppings on shelves and in a packet of cereal, the shells of fly pupae, and a packet of sugar that had been gnawed by rodents.
The visit, on 27 May last year, also turned up spilt food and rotting coriander in home delivery trays.
"It beggars belief that a national retailer would allow food to be stored in an environment where rodents are running riot," said Daniel Anderson, Enfield Council's cabinet member for environment.
"It is simply unacceptable for customers to be exposed to the potential risk of harm because a company cannot get its house in order and store foodstuff in a safe and hygienic manner."
Asda, recently voted the country's worst supermarket in a Which? survey, has apologised and said it had carried out a review of food safety processes, including its pest control.
A spokesman said: "The conditions found at our Enfield home shopping centre in May 2016 were completely unacceptable and we are deeply sorry that on this occasion the strict processes we have in place failed at a local level.
"We would like to reassure all our customers that immediate steps were taken as soon as the issue was flagged last year to restore the high standards that our customers expect from us."
Asda admitted three food safety and hygiene breaches and was also ordered to pay £4,843 costs.