ZAC GOLDSMITH lurches into view, his tall, handsome form contorted as he struggles with a roll-up. Even green billionaires have vices. He slumps on to a sofa at the Bluebird Café in Chelsea and glances at the camera. As the son of the late Jimmy Goldsmith, the brother of Jemima Khan, and now pin-up for Conservative greens, he has been photographed a thousand times. But he is not at ease with it.

This diffidence sits oddly with his tenacity in campaigning, a stubborn courage perhaps inherited from his father and his uncle, the environmentalist Teddy Goldsmith, who founded the Ecologist magazine that Zac now edits. Today the 31-year old is fresh from a battle over aspartame, the sweetener, that the Ecologist has criticised.

“How did aspartame get on to the market? Every study by industry has shown a clean bill of health — every study not funded by industry has revealed problems,” he says. “It had a hard time getting through the regulatory system but magically it got on to the market. The regulatory system is working against us.”

The magazine has stood up to some tough corporations, notably Monsanto over GM foods. “They did everything to try to stop us,” he says. “They put pressure on the printers, the shops.” The clash is legendary in green circles: in 1998 the magazine’s printer of 26 years pulped its Monsanto issue without warning. “I had to buy a printing firm for the night to take responsibility for whatever happened. Then no wholesalers would take it — and we made that into a story. But Monsanto propelled us into a different league, from selling 5,000 copies to over 500,000. They ordered 18 copies. I was very excited, but I was more exhausted mentally than I’ve ever been. That was when I realised I couldn’t do it alone — I needed a team.”

He acknowledges that his fortune puts the magazine in a privileged position. “We don’t have shareholders and we don’t need to make a profit.” He is acutely conscious that he can afford to be conscientious. “I’m lucky that I’m able to grow my own food (on his organic farm in Devon) and to employ someone to do it.” And he is at pains to say that he does not live a model lifestyle.

What does he think the rest of us should do? “It’s not about living like a monk,” he says. “The single most important thing is to buy local food. That’s more important than buying organic, although I support organic. Buying local actively minimises dependence on oil. It’s healthier, fresher and it puts money into the local economy, not to a middleman.

“We lost 52,000 farmers and farm workers in 2004 — about 20 per cent of the total. It’s terrible to think that we’re losing our farm base but at a political level no one sees that as a problem.

“People roared with laughter when the Prince of Wales talked about organic farming — now half of families feed their kids organic. Yet still only the well-off can afford it. No economist can explain why local food is more expensive.

“The idea that we should depend on imports for food is madness. Why do we throw milk away but still import it from Germany? Why do we sell as much poultry meat to the Netherlands as they sell to us? There is a perversion that favours ever-increasing distance between producers and consumers. Some experts think I’m neurotic. But would you gamble the life of your child that there will be no war, that the world’s breadbaskets will provide all our food, that the oil to get it here will continue? You can’t.

“The Punjab was India’s breadbasket and now it’s more than 50 per cent desert. China’s northern plains produce two thirds of its grains, but they’re shrinking by 10,000 square metres a year. The water table is collapsing. There are real environmental problems. China became a net importer of grain for the first time a year and a half ago. And we’re facing an oil crisis. Look at China’s thirst.”

The man who has been mocked as a gentleman farmer playing with tractors is not claiming a natural affinity with the land. “I bought a farm in Devon and I read every book on farming and I turned up thinking I was an expert. I even felt like a farmer for a short period of time, until I was standing next to a man who was semi-literate, and I was totally useless. I remember trying to milk a cow and faffing about and it was very obvious. Academic knowledge is no substitute for what he has: he learnt from his father before him and his father before that and he knows more about that land and what grows there than anyone in the world. And he can communicate with the animals. I walk into my field of cows and there is this incredible hostility. He walks in and is greeted as a friend.

“There is no value placed by society on those kinds of people — my neighbour made £9,000 last year and had to employ a part-time secretary to help to understand the new regulations.”

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