Rising fuel and crop prices and growing global competition for food mean we should take British farming far more seriously

Oil breached the symbolic $100 a barrel mark last week. OK, it was the action of a solitary small trader, making his mark and optimists are confident prices will fall. But others disagree. And this adds to consumer uncertainties - which makes the promise of cheap food look ever more precarious.

Commodity prices are rising just when we should be investing massively in more sustainable food systems. The Standard & Poor commodities index rose 31% last year, its "best" performance for 26 years - but as we all know, what's good for dealers spells trouble for consumers.

Cheap food is under pressure from climate change, farmer conversion to biofuels, population growth, global water shortage, and rising demand from developing countries that are getting wealthier. Take China, where food prices rose 18% last year alone.

If a billion more people eat diets like ours - containing more meat, dairy fats, soft drinks and sugary processed foods - and aspire to drive cars, can the earth take it and won't inequalities rocket? However you look at it - and whatever Marks & Spencer might say, the planet needs a plan B.

The Oxford Farming Conference's call to stop the slide in home-grown food supplies may look like nothing more than special pleading from farmers.

But I urge caution before we reject it. A new politics of food security is without doubt emerging.

There are a number of hot policy questions that need answering. What is a sustainable food and diet system? What's the best use of land - is it food, fuel, amenity, carbon sequestration or all of the above? How can we marry low carbon, calories, water and waste?

Defra economists argue Britain is rich and can buy on world markets. But what's the moral compass behind that, any more than current reliance on pursuing cheaper land and labour?

Markets look orderly until there's a crisis, when the price of dependency can be high. The UK only paid off its US 1941-5 Lend-Lease food bill in 2006. Some mortgage horizon.

True, we are a long way off World War Two dependency. In 2006 the UK was 63% self-sufficient for total food and 73.3% for indigenous foods, while in the 1930s, home-grown food accounted for only 30-40% of the need.

By that benchmark, we are far from crisis. But at what point does it become risky? And if the food industry agrees with government policy, is it prepared to tell the British to 'dig for victory' some time too?n

Tim Lang,

professor of food policy,

City University