Consumers across the UK have fallen foul of supermarket giant Sainsbury’s, it was revealed earlier today [Thursday], after an investigation by a national newspaper found that chicken breasts are being sold with altered “use-by” dates.

Allegations made by an employee at one of the retailer’s suppliers prompted the Guardian investigation into the giant Devon-based Lloyd Maunder poultry plant, which provides a fifth of all Sainsbury’s fresh chickens.

The newspaper claims to have found replacement use-by labels fooling consumers into thinking that the chickens had an extra 48 hours of shelf life. Furthermore, it found that the portioned chicken was actually sourced from a Wolverhampton firm, GMB Meats, which is not approved as a Sainsbury’s supplier and buys meat from Europe. On Sainsbury’s shelves the meat was labelled “British farm standard”.

Alistair Ross, MD of GMB, told the newspaper that he thought the chicken was intended for catering use only. Furthermore, he revealed that he could not guarantee the meat was British because the company imported meat from integrated Dutch and Belgian suppliers.

Andrew Maunder, a director of Lloyd Maunder, meanwhile said that the chicken purchased from GMB to be repacked for Sainsbury’s was actually meat originally sold to GMB by Lloyd Maunder: “It is our understanding that the product supplied to Sainsbury’s is not only British but from our own source.”

Last night, Sainsbury’s said it was shocked and would launch an internal inquiry, not least on the presence of an unapproved sub-supplier. The firm insisted that the chicken breasts, which were sold as part of a “buy one, get one free” offer, were tested for safety and are no longer on sale. A spokesperson added: “We are shocked that a supplier of ours has broken our agreement and used other companies to portion chicken without our knowledge.

“We pride ourselves on the integrity and traceability of our food and take this extremely seriously.”