From big dig to today’s big issue - how healthy food is big business

"Grow your own" then became the buzzword. The stables in Hyde Park became home to a large herd of pigs. Allotments were dug on every available green space. Every month the Ministry of Agriculture would send out a newsletter advising on what to plant to get maximum benefit from the soil.

We didn't have fossil fuel fertilisers so crop rotation was vital — in the same bit of soil, potatoes and root crops were planted in year one, peas, beans, onions and leeks in year two, brussels, broccoli, cabbages and kale year three. Feburary, the newsletter said, is a good time to sow broad beans, spinach, to plant shallots and Jerusalem artichokes and divide rhubarb.

By 1943, 70 per cent of Britain's food was produced at home and only 30 per cent was imported. I am excited because, with advice from museum curators, we're going to replicate two wartime allotments following the guidelines in the monthly newsletters.

This healthy food vision is different from the scenario spelt out in Food Inc, a new film made by American authors Michael Pollan and Eric Schlosser. Today's business is dominated by a few multinationals such as US giant Cargill, which controls up to 45 per cent of the world's grain. To such companies the process of rearing animals and growing crops is no different from any industrial production.

This industrialisation might have led to endless cheap food but it has come at a price. Increased outbreaks of e-coli, obesity and a generation of kids where 26 per cent enter primary school already obese with a high chance of developing type 2 diabetes.

The US government continues to subsidise crop farmers (soy, grain and corn) at the expense of vegetable growers, which means it is cheaper to buy a 99-cent hamburger than a head of broccoli ($1.30). The desire for good food is not only a middle-class pursuit — in the film, a Mexican-American family who would like to eat the broccoli can't afford it. The father is an overweight diabetic and his pills cost $200 a month. They eat hamburgers.

But the consumer is king: every time we buy a product we're casting a vote for change. Even Wal-Mart now sells vast quantities of organic yoghurt.

After the film premiere on Monday, Sainsbury's CEO Justin King told me. "In 2007 we went fully fair trade with our bananas and we still sell just as many. It saved the banana industry of the Windward islands". Indeed, so pleased were the islanders that when King visited the Caribbean he was carried across the room by the Prime Minister to say thank you!