A potato buyer for Sainsbury's has been arrested over allegations he took £3 million in bribes from a supplier.
Buyer John Maylam was questioned by police over accusations he received money from Greenvale, a producer. A member of Greenvale staff was also arrested.
The firm, which provides about half of the grocer's potatoes, said it raised the alarm after an internal investigation roused suspicions.
A police spokesman said: "City of London police executed and completed search warrants at two residential addresses in Cambridgeshire and Shropshire and two business premises in Shropshire on Thursday March 13th.
"Two men were arrested on suspicion of corruption and money laundering and were subsequently bailed."
A Sainsbury's source told the Times newspaper: "We are the victims of an alleged crime and take it very seriously.
"None of the payments went through our system and we believe this was limited to the one supplier."
Mr Maylam has been with Sainsbury's for a decade and has been used as an expert commentator by the supermarket chain.
Greenvale, which also supplies Tesco, has potato packing operations in Shropshire, Cambridgeshire and the Scottish borders.
The news highlights the controversial relationship between Britain's largest supermarkets and their suppliers.
Farmers and small retailers have complained the large chains have too much power to set prices and the Competition Commission is investigating the issue in its report on the grocery market which is due out next month.