The CBO estimated how much of the rise in food prices between April 2007 and April 2008 was due to an increase in the production of ethanol - and their figures show that expanded production of ethanol contributed only between 0.5 and 0.8 percentage points of the 5.1pc increase in food prices measured by the consumer price index.

Over the same period, other factors had a greater effect on food prices than did the use of ethanol as a motor fuel.

"The report released by the Congressional Budget Office confirms what we've known for some time – the impact of ethanol production on food prices is minimal and that energy was the main driver in the rise of food prices," said Growth Energy CEO Tom Buis.

"But now that corn and energy prices have fallen dramatically, we hope CBO will look at why grocery prices have not dropped accordingly.

"Growth Energy has called on Congress to investigate food prices so we can get to the bottom of this issue," Mr Buis said.

Energy prices do seem to be the major culprit in raising the price of food.

After examining approximately 25 food price studies and conducting their own analysis, a team of economists at Purdue estimated that energy prices accounted for 75pc of the increase in corn prices.

Excessive speculation in the commodities market also played a significant role, helping to drive up the costs of almost every commodity traded, including corn, coffee, and crude oil.

The CBO report also looked at ethanol's role in reducing greenhouse gases and the amount of gasoline consumed.

Using data from a study conducted by the Argonne National Laboratory, the report said that the production, distribution, and consumption of ethanol will create about 20pc fewer greenhouse gas emissions than the equivalent processes for gasoline.

It also found that use of ethanol reduced gasoline consumption in the United States last year by 4pc.

For 2008, such a finding translates into a reduction of about 14 million metric tons of carbon dioxide and equivalent gases.