The Competition Commission has sent out legal notices to Asda and Tesco demanding access to e-mails sent to suppliers over the summer, to cast light on their relationships with suppliers.

Reports in The Sunday Telegraph said the Comission wanted to see all e-mails over a five-week period around June, to investigate allegations that suppliers were faced with blacklisting if they did not provide discounts.

A Competition Commission spokesman told British Baker: "We are not going into details about what we are looking into, but one of the strands of the investigation is looking at how supermarkets treat suppliers."