"The fines are dwarfed by the huge profits made by these retailers," he said. "An opportunity has been missed to make them stop and think about the way they do business. If nothing else, though, it proves that they do not really have their customers' interests at heart, despite their claims to the contrary."

Sainsbury's posted an operating profit of £232 million in the 28 weeks to 6 October, an increase of £38 million compared to the same period in 2006. The US retailer Wal-Mart, which owns Asda, saw pre-tax profits rise to a staggering £1.4 billion in the three months to October.

The supermarkets fell foul of the Competition Act 1998, which prevents businesses from colluding in a way that harms competition in the UK. The OFT reported that customers were being charged 15p extra for a quarter-pound of butter, the same per half-pound of cheese and 3p extra per pint of milk.

All of the supermarkets and dairies which admitted liability have argued that their actions were designed to aid British farmers, who were reeling from the effects of the outbreak of Foot and Mouth disease. However, the FPB agrees with the OFT's findings that smaller producers did not benefit from the higher prices paid by consumers.

Tesco, Morrisons and the dairy processor Lactalis McLelland are also alleged to have fixed the price of dairy products, but do not accept liability. They will make representations to the OFT before it makes a final decision.