The following correction was printed in the Observer's For the record column, Sunday June 24 2007

The article below used a quotation which linked Monsanto to seeds which 'include a terminator gene so they can't be replanted'. This is not true; to date, there are no such seeds in existence, and Monsanto is committed not to use or commercialise such technology.

Not since Jesus rustled up a feast from some fishes and a few loaves of bread - beat that, Nigella - have we invested food with such spiritual qualities; and if food has become the faith of a decadent West, its high priest is Carlo Petrini. When the founder of the Slow Food Movement met the Prince of Wales last week it was hard to say who was having the audience.

Ditto when the Italian campaigner and writer met the Conservative leader David Cameron, and David Miliband, the Environment Secretary. When in America Petrini might pop in on Barack Obama or Al Gore. Time has included him in a series of 'European heroes', who created the 'ethical consumer'.

Petrini came to prominence two decades ago when he stopped McDonald's opening by Rome's Spanish Steps. His non-lethal weapon of choice at the time? Plates of penne. But does he have a bigger point, or is he merely a kind of modish Dalai Lama figure for those who think nothing of paying a small fortune for purple broccoli, dusted with powdered linseed or potatoes sold 'with added earth' from Kensington's new and uber-fashionable emporium, Whole Foods Market?

Prince Charles certainly seems to find more in him. Petrini has become the Prince's new guru. As Charles led him around Highgrove, the interpreter grew embarrassed, so matey did the two seem, with the normally formal heir to the throne greeting the campaigner as 'My dear Carlo'. Several peers were kept waiting as Petrini's audience over-ran. The two are now in constant correspondence and are planning another meeting later this summer.

During this, his only interview while in Britain, Petrini reveals he has moved on from agitating against McDonald's and instead urges us to rise up against Monsanto for patenting seeds which he condemns as 'violence' against the developing world. He declares French food to be in a worse state than ours, which will cause consternation across the Channel. He also has harsh words for the celebrity chef culture, obsessed with 'recipes, recipes, recipes'.

Indeed, for one so idolised by the privileged, his views are radical. He is more likely to tell you about the ingredients of a just agrarian society than the perfect artichoke risotto. The Slow Food Movement, opening its first branch in Britain, boasts more than 80,000 members worldwide. He has organised countless small-scale agricultural projects to bolster regional gastronomic traditions, and is leading the growing debate about the ethics of food, spreading his message that it should be delicious, environmentally friendly and socially fair. Which is a big task for a quarter pounder.

For one who believes in slowness, he is always on the go. He has founded a school of gastronomy in Italy and is bringing to Britain his increasingly successful American campaign to ensure every school has a garden - all of which is pretty impressive for an erstwhile radio journalist. He must make an unlikely friend of Charles. 'I consider him the patron of the Slow Food Movement, our spiritual guide,' Petrini replies passionately. 'He has been a visionary, with his passion for organic production and a harmonious relationship with nature.

'People thought he was just romantic, a poet, and that his approach wouldn't have any economic impact; but his way is the only salvation for the planet. Those who said he was not a practical soul should now apologise.'

Amid the charm there are sharp points. So while he enthuses about Miliband as a future Prime Minister, he criticises plans to ease restrictions on supermarket building on the edge of towns. 'You cannot separate food production from the environment,' he says. 'We need to re-localise food and avoid food miles.'

He does not look like anyone's caricature of a gastronome: thin, serious and faintly abstemious, eschewing breakfast at his boutique London hotel in favour of filter coffee. 'I am a gastronome,' he smiles. 'Not a glutton. Being a gastronome can actually mean eating less, but better.' The only hint of his passion lies in his gold lapel badge of a snail, reflecting his belief in the languid rhythms of Mediterranean life.

Still, as he grows more expansive, you can easily picture him on a terrace scented with bougainvillea, sipping Barolo. He says you must, every day, eat dinner with the one you love. He contrasts his ideal, in classic Italian style, with the reality: 'A woman cooks some food, and no one smiles at her or says "thank you". Neither is there any fascination with food. In Mediterranean Europe, there is still that conviviality, that ritual. The most important thing about eating is to enjoy the moment of affection. A civilisation that loses this becomes very poor.'

This is a hard sell to a nation fed from the Tesco ready-meals aisle. Yet Petrini does not merely argue about supermarkets; he works to save traditional foods by setting up local networks, be it for Cornish pilchards, Malaysian rice or Greek cheese. Nor does he re-hash the usual condemnations of globalisation, instead arguing that learning about and helping other cultures fosters 'a virtuous globalisation'.

He does not always paint the little guy as victim - keepers of small shops must shape up. 'They must become cultured people,' he says 'who can talk knowledgeably about food and how it is produced.' It is certainly optimistic to envisage Arkwright from Open All Hours ruminating on the production values of polenta. 'I like to imagine the hands of the people who grew the food, transported it, processed it and cooked it before it was served to me,' he says.

How has Italy largely avoided Tesco-fication? 'We have supermarkets too,' he says. 'But we have the ancient tradition in every small town of a market. The further north you go in Europe, the weaker that is.' Does he detect much progress in Britain? 'Choice has improved, but I'm sceptical of the real quality.

'Still, France has suffered even more than England with the growth of these huge supermarkets like Carrefour. I know English people have this romantic idea about Provence, but in many places in France the agrarian ideal has become a memory.'

If that is true even in the land of the slow lunch, as captured by Manet, isn't his movement a nostalgic distraction for wealthy, leisured foodies rather than a manifesto for our grittier, busier age? 'We need to educate people. Food is not too expensive, it is too cheap.'

Hmm. Statistics out on the day of our interview said the recent rise in inflation was caused almost entirely by food prices: for the single mother in a tower block it probably doesn't seem that cheap. 'In Italy people spend 12 per cent of their budget on food, and 10 per cent on cell phones. It used to be accepted that food would be our biggest expense. So in the scale of our values we have to restore food.'

It does not help prices, he says, that gaining organic registration is expensive and cumbersome for farmers, so 'absurdly' the system favours farmers who make least effort. Prices are also pushed up by an insistence on buying produce flown to shops out of season.

If European Union farm policies are 'disastrous', America, he believes, has made 'even more dramatic choices, with less than 2 per cent of its population left tilling the soil'. As for President Bush pushing bio-fuel, Petrini dismisses the notion that 'land can become the new oil field'. But he says there are encouraging signs in America, with a small band of converts setting up slow food agricultural enterprises.

With starvation in the southern hemisphere and poor diets in the northern, he has scant interest in the twitter of celebrity chefs, whom he dismisses as 'reductive'. 'Slow food tries to show people that gastronomy is about economics, anthropology, biological and genetic science.' Rather than making another lamentable reality TV show - 'pornographic bombardment' - Gordon Ramsay et al should 'go and cook in some care homes'.

He is pleased McDonald's has not had a major breakthrough in Italy, but his attention has shifted: 'I'm much more concerned about firms patenting seeds that have been passed down from generation to generation. For me, to rob the people is a criminal act. That's a lot worse than McDonald's.'

He plans to set up a giant database of seeds to undermine patenting, which started when America's patent office gave permission for the practice, endorsed by the World Trade Organisation. 'So in Mexico, birthplace of corn seeds, farmers have to pay patents to multi-nationals for new hybrids.'

Monsanto et al would, no doubt, say they have to invest large sums developing such seeds. 'These seeds include a terminator gene so they can't be replanted. It is violence. You can decide whether to go to McDonald's but you can't decide whether to use seeds. It is bio-piracy. And now natural herbicides are being patented and sold for fortunes in supermarkets without giving any royalties to people in third world countries who discovered and developed them.'

How much of this will David Cameron swallow? And does Petrini back the new, cuddly Tory leader? 'We tend to give credit to anyone who shares our ideas, though I naturally feel more affinity for the Labour party,' Petrini says. 'We shall suspend judgment until and if Cameron gains power.' But it is Miliband who excites him: 'I am following him with great interest. I think he has enormous promise.'

So in half a century will the world have slowed to the melodious, civilised saunter of the Slow Food Movement, or will it have sped up into a fast food, disposable hell? He laughs: 'I think it will be a huge achievement if in 50 years humanity even exists. The environmental destruction of our ecosystems is that dramatic. But man has a choice and I hope he will make the right one I hope he will choose virtue.'

Take it easy

The Slow Food movement was founded by Petrini in Italy in 1989. It began as a response to the proposed opening of a McDonald's in Piazza di Spagna, Rome. It has more than 80,000 members in 100 countries. Slow Food UK has more than 2,000 members. The movement supports products under threat such as Canada's Red Fife wheat, Morocco's Argan oil and the Netherlands' Eastern Scheldt lobster. In the UK it backs Three Counties perry in the West Midlands and Cornish salted pilchards.

Slow Food movement tenets

'We believe in the diversity and locality in food and drink and that everyone has a fundamental right to pleasure and consequently the responsibility to protect the heritage of food.'

'We believe that food should taste good, be produced in a clean way that does not harm the environment, animal welfare or our health.'

'We believe food producers should receive fair pay for their work.'
Rowan Walker