Organic vegetables and other crops "won't deliver sustainability" because their lower yields mean that more produce has to be grown elsewhere, according to Professor Tim Benton of the University of Leeds.
Benton, who took up the position of global food security champion last November, was speaking at the conference Food Security: The Value of Vegetables, held at the Warwick Crop Centre in Wellesbourne last week.
"We have to drive land harder to get more out of it per unit area - we don't want to convert the remaining rainforests into agricultural land," he said.
"But the Common Agricultural Policy is driving us to 20 per cent organic production. That would have to be made up for by a further 10 million hectares of land outside the EU, driving intensification and bringing environmental consequences."
He added that a similar principle applied within the UK. "If you drive East Anglia to produce more food, you can be less intensive in, say, the West Country."
Benton also dismissed as a red herring the argument that imported food carries unacceptable food miles. "Different areas grow different things better. Local food production isn't necessarily the most efficient."
However, this view was challenged by Agritec International managing director Peter Gresty. "There is so much more we could grow in the UK rather than shipping it from Kenya," he insisted.
Philip Effingham of Greentech Consultancy agreed. "There is a lot of potential to replace imports at both ends of the season," he maintained.
He said the problem lay not with the inefficiency of organic production but with the high volume of waste across the fresh produce sector, both in the field and on the shelf.
"Retailers commit all manner of sins that prevent customers picking up the product," he said. "But we also need varieties that keep longer and stand up to the rigours of the supply chain."
Sustainability is impossible to define or measure, Professor Tim Benton of the University of Leeds also told the food security conference. "In practice, you trade off many things against each other," he said. "Industry likes carbon footprinting, but it's just one aspect."