TODAY marks the start of a new annual event that should be of immense interest to all who care about the quality of food. 'Organic Harvest' is a celebration of the best of naturally grown foods. Across Britain during October there will be events such as farm open days, tastings and price promotions on everything from organic baby food to beer.

My correspondence with Independent readers shows that many people are worried about the nature of our 'conventional' food supply, whether over the treatment of animals in factory farms or genetic 'modifications' of everyday foodstuffs. The occasional insights we get into intensive agriculture are not reassuring.

Last autumn, for example, a leaked government memo admitted that about 10 per cent of UK-grown lettuces contained residues of chemicals which indicated 'a misuse of pesticides'. It reported that several banned chemicals had been found, as well as an excess of permitted ones.

Until quite recently, organic food was largely dismissed. High prices (an average 16 per cent more than conventional food) and a cranky image limited its appeal. Organic farmers have been handicapped by the subsidies paid to farmers in Europe, which favour quantity over quality. Meanwhile, powerful supporters such as the large chemical and bio-tech companies have been backing conventional producers.

The notion that organic food is of higher quality is something advocates of conventional farming strenuously deny. Buy organic food because it is better for the environment, if you like, but do not kid yourself that it is superior - so their argument goes. But a growing body of evidence suggests otherwise.

Earlier this year, another leaked document - a comparison of conventional and organic fruits and vegetables commissioned by the Ministry of Agriculture, Fisheries and Food (Maff) but subsequently suppressed by it - showed that the organic apples and tomatoes were richer in vitamins. Organic carrots were also richer in the health-giving trace element potassium.

These results echo findings of Danish researchers in the Seventies which showed reduced water content, reduced nitrate (a carcinogen) levels and increased vitamin C in organic potatoes. The French government research institute, Inserm, compared the two types of food in the late Eighties. It, too, found that the organic samples contained less water, more dry matter and substantially higher levels of beneficial minerals and trace elements.

Organic vegetables in the tests contained, for example, 49 per cent more magnesium and 290 per cent more iron than the non-organic. That does not surprise advocates of organic food, any more than the finding by Danish researchers that men who eat organic food are twice as fertile as those who do not. It may be no coincidence that, according to reliable research, male fertility worldwide has dropped by 50 per cent in the past 50 years.

And what of taste? Might it be that all those precious nutrients help it along? Last time an independent tasting panel carried out a comparative blind tasting of various conventional and organic foods, the organic foods fared much better.

In contrast to chemical-based agriculture, organic farmers use sensible crop rotations and natural pest- control methods, and only natural composts and animal manures are used as fertilisers.

This is quite different from the growing number of 'half-way house' systems, better known as 'integrated crop management'. These schemes at best represent the more acceptable face of chemical farming; at worst, they are little more than a way of allaying consumer concerns. Growers can resort to the spray-can when over-cropped soil shows signs of sickness; organic farming is geared to prevent problems by building up the basic fertility of the soil.

If the treatment of farm animals worries you, the Soil Association (the main certifying body for organic food) operates a tough set of animal welfare standards.

Unfortunately, organic food is hampered by price. It would take a reform of the EU Common Agricultural Policy to change that. It is up to consumers to insist that the question of natural, healthy food be put high on the political agenda.

This week's Organic Harvest events include:

Jonathan Dimbleby gives organic movement's annual Lady Eve Balfour Memorial Lecture on integrating food production with care of the environment, on Monday at 7.30pm in the Natural History Museum, London. Post-lecture Harvest Supper by chef Sally Clarke (price pounds 45).

Organic commuter breakfast at Waterloo station on Monday attended by John Gummer, Secretary of State for the Environment.

David Bellamy hosts organic lunch and tasting at Boots Herbal, Merrial Street, Newcastle-under- Lyme, Staffordshire, on Monday.

Heeley City Farm, Sheffield, Autumn Show, today.

Leslie Kenton speaks on organic food at Trinity College, Carmarthen, on Wednesday.

Organic Harvest line: 0272 299988.