Watson told the Oxford Farming Conference that biofuels production from sugar cane in Brazil may be one of the only sustainable current methods.

He added that there needed to be aggressive research and development and in five to 10 years time it was possible that new, better technologies could be commercially viable.

Crispin Tickell, director of the Policy Foresight Programme at Oxford University's James Martin Institute of Science and Civilization, said US ethanol policy had been "disastrous."

Tickell, whose former posts have included Chef de Cabinet to the President of the European Commission and President of the Royal Geographical Society, said more attention needed to be paid to renewable energy sources such as solar and geothermal.

"Biofuels have a role to play but only as one of a number of technologies," he told the conference.

CLIMATE CHANGE NEGATIVE FOR FARMING

Watson said climate change in the short-term was favourable for UK agriculture, lengthening the growing season but overall would be detrimental for the farming sector.

"A changing climate overall is likely to be negative for the agricultural sector and demands a significant amount of adaptation," he said. Some have cited genetically modified crops, such as new drought resistant crop varieties, as key to adapting.

"Clearly it has potential but we need to look at it on a case by case basis," Watson said, warning however that some developing countries may be concerned about becoming dependent on seed companies such as US-based Monsanto.

Watson said farmers needed to be paid for environmental services such as capturing carbon or helping produce fresh water supplies.

"Agriculture is more than production," he said.

Tickell agreed, adding that agricultural markets "should operate within a clearly defined framework of public interest."

"We should accept that agriculture is not a business like any other and it is a mistake to regard it as such," he said.

Tickell said there also needed to be greater focus on human diets involving more plants and less meat.

"We need to look at the healthy diet which on the whole we have tended to abandon," he said, noting the current concern about obesity in Britain. "Greater consumption of meat in India and China has already driven up feed costs," he added.