The Competition Commission has ordered Tesco and Asda to produce the contents of more than 11 million e-mails, as the investigation into claims that they used bullying tactics against suppliers is stepped up.
Both supermarkets deny exerting undue pressure on producers and say it could take weeks to provide investigators with the correspondence.
The regulator has demanded to see the material amid reports that it has already found evidence that suppliers allegedly received threatening e-mails and telephone calls as Adsa and Tesco were engaged in a price war.
The e-mails, from a five-week period around June this year, are thought to contain demands for discounts with the threat, implied or otherwise, of being dropped.
Under the supermarket industry code such practices are banned but it is feared that farmers and other suppliers are too scared of losing contracts to complain.
The supermarkets insist they have nothing to hide. Asda says: “We adhere to the code of conduct between suppliers and supermarkets.” And Tesco says: “We are doing what we can to assist the commission with this enormous data request.”
The Competition Commission is due to issue findings of a wider investigation into the dominance of supermarket giants Tesco, Asda, J Sainsbury and Wm Morrison in the grocery market by the end of September. This latest development is expected to delay the announcement.