Biofuels have caused world food prices to go up by 75%, according to a new report from the World Bank.

A leaked copy of the report contradicts US government claims that using plants to produce fuel contributes less than 3% to food prices.

It was claimed today that the the analysis - carried out by a respected economist at the global financial body - has not been published to avoid embarrassing US President George Bush.

The leaked study reportedly concludes that income growth in developing countries was not a major factor in food price rises, while successive droughts in Australia had only a marginal impact.

Instead, it argues that the EU and US drive for biofuels has had by far the biggest impact on food supply and prices.

"Without the increase in biofuels, global wheat and maize stocks would not have declined appreciably and price increases due to other factors would have been moderate," the study is reported as saying.

"The basket of food prices examined in the study rose by 140% between 2002 and this February. The report estimates that higher energy and fertiliser prices accounted for an increase of only 15%, while biofuels have been responsible for a 75% jump over that period."

Biofuels - derived from crops such as corn, rapeseed, palm and soya - as an alternative to petrol and diesel were seen as the environmentally-friendly solution to global warming and rising fuel prices.

The high-profile international issue is due to be discussed by G8 members next week in Japan.

Today's report also comes ahead of the Government releasing its own report on the impact of biofuels by Professor Ed Gallagher, head of the Renewable Fuels Agency.

On Monday, shadow agriculture spokesman James Paice let slip during a Parliamentary debate that the Gallagher report found increasing production of biofuels was "not sustainable".

In Tory-led debate on food security, Mr Paice was challenged to set out Conservative policy on biofuels.

He replied: "The issue of biofuels has to be based on sustainability. It's quite clear in the Gallagher report last week - or whenever it was - that it's not sustainable."

The review was commissioned by Transport Secretary Ruth Kelly in February to look into concerns that biofuel production could have an unwanted side effect of raising global food prices.

On Monday, MEPs will vote in the EU Parliament's Environment Committee on proposed amendments to the Renewable Energy Directive, including an amendment to scrap the target to source 10% of transport fuels from biofuels by 2020.

Responding to the leaked study, Friends of the Earth biofuels campaigner Kenneth Richter said: "This report shows that when MEPs vote on biofuels targets next week they will have the fate of millions in their hands.

"Finding enough land to grow 10% of Europe's transport fuel will lead to more hunger and suffering - as well as doing next to nothing to reduce carbon dioxide emissions.

"Politicians must act responsibly and change course on this disastrous transport policy."

He called on MEPs to scrap biofuels targets and vote instead to double the fuel efficiency of new cars by 2020, which he said would do more to reduce dependence on fossil fuels.