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The food chain contributes 18% of the UK's greenhouse gas emissions and agriculture makes up around half of this. Wheat production has a lower carbon footprint than the livestock sector, but milling, bread-making, packaging and retailing all produce further emissions.

Nitrogen fertiliser is a cause of many of the agricultural emissions. About three million tonnes of fertiliser are used each year in the UK, about half of which is imported. The raw material for fertiliser is petrochemicals (usually natural gas) and the energy-intensive manufacturing process causes significant emissions of both carbon dioxide and nitrous oxide, another greenhouse gas 300 times as powerful as carbon dioxide.

How does organic wheat production compare? Better, it seems, as it is both more energy-efficient and conserves the soil's organic matter. Detailed studies carried out for Defra have calculated that organic wheat production uses about 16% less energy per tonne, mainly because it does not use nitrogen fertiliser.

Instead, organic farming uses a natural process of fixing atmospheric nitrogen with legumes such as clover. This means the ultimate energy source for organic crops is renewable solar energy, not fossil fuels.

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