The news comes at a critical point in the world's negotiations on biofuels policy. Leaders of the G8 industrialised countries meet next week in Hokkaido, Japan, where they will discuss the food crisis and come under intense lobbying from campaigners calling for a moratorium on the use of plant-derived fuels.

It will also put pressure on the British government, which is due to release its own report on the impact of biofuels, the Gallagher Report. The Guardian has previously reported that the British study will state that plant fuels have played a "significant" part in pushing up food prices to record levels. Although it was expected last week, the report has still not been released.

The leaked World Bank study disputes that: "Rapid income growth in developing countries has not led to large increases in global grain consumption and was not a major factor responsible for the large price increases."