Five major British supermarket chains and five processing companies fixed prices on dairy products, adding hundreds of millions to consumer bills, the Office of Fair Trading said Thursday.
In a preliminary finding, the agency said Asda, Morrisons, Safeway, Sainsbury and Tesco and dairy processors Arla, Dairy Crest, Lactalis McLelland, The Cheese Company and Wiseman shared sensitive data on milk, butter and cheese in 2002 and 2003.
"The OFT has provisionally found that this practice was harmful to consumers by restricting the competitive process, leading to higher prices," the agency said.
"The OFT also believes that the parties understood their actions might be anti-competitive and in fact retailers were previously warned of this by the OFT."
The agency estimated that the alleged price-fixing added 270 million pounds (388 million euros; $542 million) to consumer costs in the two years.
The supermarkets and processors will be given an opportunity to respond before a final ruling is made, the agency said.