The Liberal Democrats have claimed that farmers are not receiving the full benefits of price increases for their products.

New research has shown that while the cost of chicken, tomatoes, eggs and potatoes rose by 47 per cent between 1985 and 2002, farmers gained just 12 per cent of the extra cash for their produce.

The proportion a farmer takes home from the retail price of these indicative "shopping basket" items has fallen by one quarter since 1985, from 46 per cent to 35 per cent.

Lib Dem food and rural affairs spokesman Andrew George said farmers were losing out to corporate interests.

"Someone must be making money here, and it isn't farmers," he said.

"People are paying more for their food, yet British farmers are not getting their fair share.

"The record of these four items is indicative of a wider trend, adding to the pressure that puts farmers and growers out of business, while the supermarkets profit."

The Supermarket Code of Practice needed to be toughened up or overhauled in order to protect rural livelihoods, George added.

"The Supermarket Code of Practice patently isn't working," he said.

"It amounts to no more than a public relations exercise on the part of the supermarkets and has failed to protect farmers.

"It's time the government intervened to ensure that farmers receive a fair share of the final retail price. Farmers and consumers deserve a fair deal."