Asda has been hit with a £300,000 ($365,673, €345,963) fine after dead mice, faeces and flies were discovered at a home delivery depot in Enfield, north London.
The deceased vermin were found in the bread section. The site on Southbury Road distributes food to online shoppers in London and Essex.
The supermarket giant was fined on Friday (3 March) and ordered to cough up costs of £4,483.61 to Enfield council.
Asda admitted to three breaches of food safety and hygiene regulations at Highbury Corner Magistrates' Court on 20 January.
The state of the depot was discovered during a site visit by food and safety officers in May 2016. Enfield Council reported that it had "found dead mice and flies in the bread section, mouse droppings on shelves and a packet of cereal and a packet of sugar which had been gnawed by rodents on the home baking aisle.
"They also found fly pupae shells under shelves; spilt food stuffs and rotting coriander in home delivery trays."
Enfield Council's cabinet member for environment, Daniel Anderson, hit out at Asda's safety standards for keeping perishables and said: "It beggars belief that a national retailer would allow food to be stored in an environment where rodents are running riot.
"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.
"I am therefore pleased that magistrates have taken a tough stance and issued a heavy penalty.
"Hopefully it will send out a strong message to all retailers that we will not tolerate them being less than properly vigilant & ensuring their staff abide by their own stated hygiene policies to protect the health and wellbeing of their customers," he added.
Asda issued an apology for the state of the depot and said it took action as soon as it was made aware of the conditions.
"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," a spokesman said.
"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."