The Durham University team say the discovery could significantly improve the yield of plants such as oil-seed rape, which can provide power and fuel.

They have identified a gene in the weed Thale Cress which can increase the production of starch and oil.

Prof Keith Lindsey, of the university, described it as a "win/win situation".

'Expensive option'

He said: "Increased dependence on motorised transport, diminishing mineral resources and increased global warming means that governments around the world are turning their attention to a range of alternative fuel sources.

"Crop plants, such as oil seed rape, offer the potential for industrial-scale renewable energy supplies - vegetable oils can be converted to bio-diesel and starches to bio-ethanol, a petrol substitute.

"But land availability, demand on water and crop yields mean bio-fuels are still an expensive option - we believe we have found a way to make bio-fuels viable."

The discovery could have huge impact on crops grown for food, particularly increasing yields in countries where good agricultural land is sparse.