Food prices have leapt 8% in two years as a result of soaring commodity costs, according to The Grocer's exclusive research.

Latest data from The Grocer Price Index shows the average cost of our secret 100-item trolley of staple products on which the index is based has risen from £169.65 in January 2006 to £183.28 this week.

Record-high grain and energy costs have boosted food prices across the board as retailers have passed on increases to shoppers.

In January 2006, the average price of an 800g loaf of branded white bread was 83p. This week it retailed for £1.10. A four-pint bottle of semi-skimmed milk now costs £1.34 but was only £1.11 two years ago. Half a dozen free-range eggs have rocketed from £1.01 to £1.39.

Wine, too, has become more expensive. A bottle of red cost £3.02 in 2006 but is now £3.12.

The price rise over the past year, however, has been less severe than in 2006 to 2007. Our basket of 100 grocery items costs 3% more than it did 12 months ago compared with a 5% rise the previous year.

"Retailers have been able to absorb inflationary pressures in the past but severe commodity price hikes and expensive fuel and energy bills have left them with no choice but to pass costs on to consumers," said James Flower, analyst at Verdict.

The Grocer 100 shows Asda has had the greater success in terms of keeping a lid on rising prices. The price of its 100-item trolley was £175.92 this week - the cheapest in the survey and 5% more than its total in January 2006.

Tesco's £182.21 trolley is 8.6% higher than two years ago. Sainsbury's, at £189.13, is 9%. Morrisons registered the biggest rise of the big four - up 10.3% to £187.51.

Nevertheless, Morrisons this week knocked rival Asda off its perch as cheapest retailer in our weekly survey of 33 products.

Asda had been cheapest retailer in The Grocer 33 for 15 consecutive weeks.