As Gordon Brown called a Downing Street summit for action to curb increases in the cost of food, the price comparison website MySupermarket.co.uk claimed that retailers were passing an increase in global grain prices down to British shoppers.

The 15 per cent rate of increase is seven times that of the Consumer Price Index, the Government's preferred measure of inflation, which is running at 2.5 per cent. The CPI is based on 120,000 prices from 23,000 shops.

The website compared prices for 24 items such as teabags, cheese, potatoes and cornflakes in Tesco, Asda and Sainsbury's. Six pints of semi-skimmed milk were 28p dearer than a year ago at all three. The price of a thick-sliced white loaf at Tesco and Asda had risen by 20 per cent, from 54p to 65p.

Eggs had gone up by 50 per cent and a bag of pasta had almost doubled in price, from 37p to 67p.

The global demand for land to grow crops for biofuels has squeezed space for crops, leaving grain stocks athistorically low levels . This has pushed up the price of grain and had a knock-on effect on the cost of livestock feed.