'I am merely the conduit,' says Patrick Holden, director of the Soil Association, when I ask him to sum up his achievement after 10 years in the job. 'The great thinkers, the founders of the organic movement at the beginning of the 20th century, had some hugely powerful ideas. All I have done is communicate those ideas to the world. That's what I think I've achieved, on a good day, with the wind behind me - and there is plenty of wind here.'

What he means, of course, is the steady intellectual wind power of the Soil Association's history and the energy and dedication of its staff - but it's easy to interpret his words mischievously. Holden, famously, can talk for Britain. In our two hours together, he effortlessly articulates issues ranging from avian flu and the vaccination of poultry flocks, to secondary metabolites (the health-enhancing compounds found in organic crops), sensitive crystallisation (a technique for measuring the vitality of food) and the relative merits of buying locally sourced produce versus fairly traded imports from the developing world.

These are the subjects - and the ethical dilemmas - that increasingly interest consumers, and Patrick Holden has played no small part in raising our awareness of them. Using parliamentary lobbying, the media, reams of scientific research and downright hounding of the food industry and advocates of conventional farming, he has plausibly expressed our collective fears about the impact of 50 years of intensive agriculture on our health and on our planet.

'There are millions of people out there who sense there is something profoundly wrong with farming,' says Holden. 'If you asked, they wouldn't be able to give a coherent account of exactly why. But if you stand in front of them and start describing accurately what you know about the consequences of industrial agriculture and the benefits of sustainable, organic farming, you are tapping into a knowledge field that they've not yet articulated but which they sense is right.'

That is why, in the decade that Holden has been director, sales of organic food in Britain have risen from £105m a year to £1.2bn. Prince Charles -his own Duchy Originals organic food range is now in most surpermarkets - believes Holden has 'contributed enormously' to the organic movement. 'The development of the organic food market over the last few years has been staggering and much of it down to Patrick's unique determination and commitment,' said the Prince this month. 'I am delighted that he has received this award from the Observer Food Monthly.'

There are 70,000 visits a month to the Soil Association's website. Last year, its booklet about pesticide residues in popular foods was requested by 30,000 people, while 40,000 - an unprecedented number - flocked to the annual Organic Food Festival in Bristol. In the wake of Jamie's School Dinners, the Soil Association is now working with 300 schools and several education authorities in its Food for Life programme - set up in 2003 to campaign for improved nutritional standards. Around 44,000 products carry the Soil Association symbol and 4,000 farms and businesses adhere to its strict organic criteria. To maintain 'equivalence' - ensuring imported foods match the Association's rigorous standards - its inspectors are active in 28 countries around the world.

As the organisation celebrates its 60th anniversary this year, it feels like its time has come. In 1988, when Holden first joined, it was very much the opposite. 'We were five people working above a shop on the other side of town,' says the tall, silver-haired 55-year-old, dressed in the trademark blazer, shirt and tie that make him look faintly ex-military. (As an organic farmer who cut his ecological teeth in a hippie commune in Wales, nothing could be further from the truth.)

'We set about building a platform for sustainable farming - organising producers, though there weren't many of them, focusing on the production capacity, the infrastructure, the means, the standards. Through the media - and we had no other resources - we tried to get our ideas across to the public. I'd say that process took 15 years.' What helped enormously were the surges of interest that occurred with BSE, foot-and-mouth and similar outbreaks. 'That's when it started to take off,' says Holden. In similar fashion, he says, the appeal of organic food right now is boosted by the threat of disasters - both natural and man-made - that could destroy our centralised, highly industrial food system and make us reliant on local sourcing. If the oil runs out, not only will transport become an issue but there will be fewer (and more expensive) agrochemicals - largely made from petroleum by-products - making organics a better choice. 'Real breakdown is so much closer than we think,' says Holden, 'whether it is a conflict, or a New Orleans-type event, or if the oil goes - all three of which are either happening or about to happen. The force has been with me, because I'm around at a time when the world is ready for these ideas.'

I know I should be interested, but somehow it is Holden's family life that fascinates me more. Twice married, he has seven children ranging in age from 34 years to 14 months, and lives part-time with his second wife on the Welsh farm he shared with his first wife (plus a handful of communards) in the early 1970s.

'I got together with my ex-wife in Hampshire,' he explains, 'and we and these friends set up a rural commune in Wales, which lasted 18 months. She already had an adopted child from her previous marriage - he's called Tom, and he calls me Dad, although he's not my biological son. Then we had three other children born on the farm and we got married in 1977, when we already had three out of the four. We stayed there until my marriage broke down in 1987.'

One of the communards, Nick Reddeck, bought the farm and leased part of it to Holden as a tenant farmer; later they became partners in the property. For 15 years, Holden spent weekends living in a converted barn and milking cows at the farm, and weekdays working for the Soil Association in Bristol. Two years ago, Reddeck left, the farm went on the market and Holden borrowed £400,000 to buy his partner out. 'During that time,' Holden adds, 'I'd met my second wife, Becky, who is 35. She now lives on the farm and we have three young children under the age of five.' They are William, four; Ben, three; and Harry, 14 months. It's a fecundity that would impress the fathers of the organic movement. While Lady Eve Balfour is remembered as the founder of the Soil Association, a charity set up in 1946 'to create a body of informed public opinion' about holistic ideas, it was two British scientists - Sir Albert Howard and Sir Robert McCarrison - who first recognised the importance of building and maintaining soil fertility, returning waste to the earth and using natural composting rather than nitrogen fertilisers.

'They were sent to India by the British government at the turn of the last century,' says Holden, 'to teach Indians how to farm and nourish themselves. They got the Hunza valley and found a population that was self-sufficient and practising sustainable agriculture. The crops the Hunza grew didn't suffer from pests and diseases; the livestock was healthy and vigorous; and the Hunza lived to 120 and were specimens of health and vitality. Howard made the connection between the quality of the food they ate and the management of the soil.'

In 1940, Sir Albert Howard published a book - An Agricultural Testimony - incorporating these ideas. 'Lady Eve [Balfour], who was the servant of big ideas, read it and immediately understood the truth of what he was talking about,' says Holden. 'Lady Eve realised that making it accessible to the public was the crucial thing.' As we talk, Holden tries to find me a rare copy of Howard's esoteric tome. 'There's one knocking around here,' he says, 'with an inscription by the author.' We settle for one with no inscription - but Holden can't wait to show me, proudly, another Bible-thick volume with red covers and yellowing pages. 'This is Mother Earth,' he says, 'the Soil Association's journal - which was a brilliant journal.'

From his manner, one would expect Holden to have a background rooted in books and academia - but in fact, his education was rudimentary. 'I come from a long line of Balliol scholars, as it happens, but I have no formal qualifications of any consequence,' he says. The son of a child psychoanalyst, he spent his formative years moving around the south east as his father took jobs at psychiatric hospitals. 'I was a loved little boy,' he says. 'I went to Dulwich Hamlet Primary School and I was head boy there. Then I went to Alleyn's, where I was thriving in a nice, sheltered, middle-class environment.'

Life changed dramatically when his father was given a professorship at Stanford University in Palo Alto, California. It was there that Holden read The Greening of America, Charles A Reich's classic about social change and 'the new consciousness'. As he drifted around California, 'doing a bit of gardening, travelling a lot', Holden felt he was at the epicentre of 'an alternative revolution that wasn't really political, more ecological', and acknowledges now that 'I was influenced by that atmosphere of thought'. In 1971 he returned to England, 'full of burning idealism, interested in communities, wanting to put this new vision into practice'. He and his friends decided to set up a rural commune, so Holden embarked on a crash course in farming. 'I answered an advertisement in the Hampshire Chronicle,' he recalls, 'which said, "Help wanted on dairy farm".'

By the age of 21, Holden was happily milking cows on the farm in West Wales where his family lives. Despite his townie upbringing, he believes, nature was always in his blood. When the commune and then his marriage broke down, Holden had what he describes as his 'second calling': working as a volunteer for the Soil Association in Bristol and, in 1995, being appointed its director. He immediately became known for his fierce intelligence, allergic reaction to authority and unstoppable rhetoric. 'Anyone who knows me well will tell you I'm prone to unfortunate public outbursts,' he says, 'where I feel that emotional thing. People say my face goes into a horrible contorted form and it's not very becoming. I've struggled with that in me, that frustration and that anger, when the world was less with us - and that was probably until about five years ago.'

He can only be referring to his legendary clashes with Sir John Krebs, then chairman of the Food Standards Agency, who appeared intractable in his view that organic food offered no clear health benefits over its conventionally farmed alternative. While that remains the official position of the FSA today, Krebs' refusal even to consider further research seemed at times almost personal. Public spats occurred, correspondence was exchanged and Michael Meacher, the environment minister, intervened in 2002 and asked Krebs to be more positive. Krebs refused and Holden retorted: 'The prejudice he is displaying is indefensible, given his position.' Peter Melchett, the Soil Association's policy director, suggested that, unless the FSA distanced itself 'from Sir John's idiosyncratic views', a more neutral body should be found to conduct research.

It was this longstanding battle that gave the Soil Association its reputation for being anti-science, a charge Patrick Holden denies. 'We live in an evidence-based society where we cannot do anything until we have proof,' he says. 'But GM and BSE have taught us that you can have intuitive feelings about things that are against nature, that don't feel right. Good decisions, I believe, are made with a mixture of scientific and non-evidence-based criteria - including intuition.'

He is sounding eerily similar to his friend Prince Charles - patron of the Soil Association and an organic farmer himself. Had Holden remained a farmer, it is doubtful the two would have met - but as he admits, being director of the Association has given him access to friends in high places.

'I recently had lunch with Justin King, the head of Sainbury's,' Holden reveals, 'as you do in my privileged position.' They talked about Holden's organic carrots, grown on his Welsh farm, which last year outsold and replaced Sainbury's own in eight Welsh stores - despite being 20p dearer. A labour of love, their packaging carries a picture of the farm painted by Holden's oldest daughter, Barley, and four paragraphs on the back, written by Patrick, explaining the merits of organics.

'I told Justin I'd like to do English stores,' he explains, 'but he said he thought it wouldn't work because it was a Welsh thing. But when they went into the English stores, sales went fantastically. It shows that people will pay more for a product with a story behind it.' Such a story, in fact, that Holden claims that his carrots are now the influence for a storyline in The Archers, thanks to his friendship with Graham Harvey, agricultural editor of the series. Within the programme, Pat and Tony Archer are marketing their organic carrots, with a picture of their farm on the packaging.

It's yet more evidence, in case it were needed, of Holden's gift for popularising organic farming. His next big task is to encourage more members of the public to join the Soil Association, making it 'the mass membership movement of the 21st century', just as the National Trust (3.4m members) and the RSPB (1m) were the most popular charities of the 20th century. 'My main focus now is making the Soil Association interesting to individuals. You would join the association to improve the quality of your life, to put you in direct contact with producers.'

If anyone can persuade people to join, the garrulous Holden can - but as the Soil Association grows larger and more mainstream, there is a danger it will lose its edge. Already, there is what Holden calls a 'worldly' relationship with the supermarkets and three-quarters of the organic fruit and vegetables sold by multiple retailers comes from abroad - clocking up air miles and undermining the local food philosphy of the organic pioneers.

'The industrialisation of organic farming is just around the corner unless we guard against it,' Holden agrees. 'Everyone wants organic food, which is great - but this is a danger for the Soil Association because the radicalism of the founders could easily turn to its opposite. There's a big discussion to be had there; I could talk the hind legs off a donkey about that.' OFM