Delivering the Amos Memorial Lecture at East Malling Research earlier this month, Professor Wyn Grant of the University of Warwick said: "There is talk of an ombudsman to redress the balance, but that won't go anywhere. Retailer power is useful to government because it helps to restrain inflation."
He added: "Oligarchic supermarkets have such a hold on the market."
Grant pointed out that government had also "handed over a lot of tasks", such as the promotion of healthy eating, to retailers.
He further argued that assurance schemes gave the supermarkets another lever of control.
"Retailers are setting their own regulations on top of the state regulations," he said. "They see themselves as proxy spokesmen for the consumer."
However, Grant claimed that anticipated taxes on unhealthy food "could be good for growers of fruit and vegetables because people will probably consume more (of them)".