Science: Why won't they let us go wild?: Seeds of native plants can help to beautify farms and motorways. But, says Patrick Matthews, Europe forbids their sale . . .

Scores of farmers will sow a technically illegal crop this autumn. They qualify for the European Union's set-aside scheme, which aims to reduce the food mountains by paying them to leave fields fallow. Instead, these farmers have opted to reseed with native wild flowers.

Left to itself, land taken out of cultivation will often look unsightly, sprouting docks and thistles. However, farmers can draw money from Brussels if they carry out environmental improvement, for example, by seeding their unwanted fields with attractive wild flowers. British companies are world leaders in bulk-producing seed originally gathered from the wild, and they see set-aside as a new business opportunity. In the process, however, they have tangled with the EU's seed regulations.

Only certain agricultural seed strains, chosen for distinctness and uniform appearance, are supposed to be offered for sale. 'Wild seed populations don't satisfy any of these criteria,' says Donald MacIntyre, of Emorsgate Seeds. 'We are breaking the law.' When Mr MacIntyre started his company in a Norfolk village 14 years ago, the last thing he intended was to sell only EU-approved versions of wild flower seed. He condemns these, as do many botanists, as a threat to native plants and insects.

The threat arises because some wild flowers, such as red clover, have been developed commercially as fodder crops. Technically, these strains still belong to the same species as wild red clover, but one botanical name can cover many variations. A single wild species can appear in widely differing forms - thanks to the genetic diversity that enabled our ancestors to conjure vegetables as dissimilar as kohlrabi and Brussels sprouts from one wild species, Brassica oleracea.

Take, for example, bird's foot trefoil, a yellow-flowered member of the pea and clover family that is the food plant for the Small Blue butterfly. Like clover, it is grown as a crop plant for animal feed. The beefy-looking specimens created for this purpose do not much resemble the smaller, sprawling forms that occur in the wild. Yet EU rules, strictly interpreted, oblige merchants such as Mr MacIntyre to offer only the cultivated version whenever a wild plant has an agricultural use.

This unintended blow to biodiversity raises issues that go beyond aesthetics. The forage variety of bird's foot trefoil is less attractive to insects such as the Small Blue. 'The problem is that if this variety is grown widely in the countryside, there's going to be hybridisation with the native wild flowers,' says Mr MacIntyre. 'It really poses a considerable threat to the butterflies and the native plant populations.' This threat is already materialising, according to Plant Life, a group led by David Bellamy that hopes to mobilise the level of public awareness that the Royal Society for the Protection of Birds has achieved for endangered birds. Earlier this year, the group put out a paper, Seeds of Destruction, claiming that much 'wild flower' seed was non-native in origin and, in some cases, no more than agricultural forage.

Its author, the botanist Dr John Akeroyd, says: 'A very real problem exists because of the use of large amounts of non-native wild flower seed.' He cited cases of 'wild flower meadows', which would pass muster with the public, but in which a trained eye would readily detect imposters. One example he gave was a much publicised conservation project on a few acres of set-aside land in the Gog and Magog Hills, near Cambridge.

Here, Dr Akeroyd found that seed bought from reputable merchants raised agricultural clover and a form of buttercup that occurs naturally no nearer than Albania. Furthermore, he says, the seeding operation meant losing an opportunity to encourage rare local plants to recolonise.

Such imports are used because demand continues to outstrip the ability of conscientious businesses such as Emorsgate to satisfy it - the company specifies that the seed is of native origin and which county it comes from.

Wild flowers are de rigueur for fashion-conscious gardeners. They also have a powerful appeal for developers and highway engineers, who wish to assure the public that scars created by earth- moving equipment can be rapidly healed. Twyford Down and the approaches to the Channel tunnel have been reseeded with native species.

The widespread use of such seed mixtures was urged in 1981 by Terry Wells, of the Institute of Terrestrial Ecology, co-author of an influential Nature Conservancy Council pamphlet, Creating attractive grasslands using native plant species. Mr Wells had observed the dullness of motorway verges compared with the land alongside railways, colonised from neighbouring fields and meadows in an era when they were still rich in wild species. He argued successfully against the Department of Transport recommendation of the time to seed verges with standard grasses and in favour of flowering mixtures.

Although he believes in using native seed where practical, Mr Wells is sceptical about the Seeds of Destruction thesis. In particular, he does not see the harm in creating what Dr Akeroyd calls 'a facsimile of countryside', given the loss since the war of 95 per cent of flower-rich meadows.

Botanists and conservationists on both sides of the argument share a concern at the staggering scale of damage done to Britain's native flora. Mr Wells does not want to be seen as suggesting that a sprinkling of seed mixture can undo or make good the destruction of historic sites. 'I'm not suggesting we should be putting these mixtures in our existing meadows,' he says. 'All I have been promoting is the use of wild flowers in sites where there are no wild flowers, like country parks, school grounds and roadside verges.'

Mr Wells is not convinced that foreign strains are taking over: 'In the case of Lotus corniculatus (bird's foot trefoil), we know the non-native form disappears after a series of wet winters. It doesn't like getting its feet wet. There's a very well-known principle of ecological sieving.'

He says there is a lack of evidence that imported strains are hybridising with native plants. 'All our legumes and grass seed have been imported from the Netherlands since the 17th century.'

The question is whether wild plants should grow where they choose or where we choose to put them. Mr MacIntyre makes it a principle to sell only the most widely distributed species, deliberately not offering, for example, meadow saffron, the wild colchicum found only in the West Country.

For Dr Akeroyd, the natural distribution patterns of even such common weeds as corn marigold should be respected. 'This plant is common on acid soils, but very rare on chalk,' he says. 'Now it's turning up all over the place.

Its ecology has been disrupted. People are groaning on about global warming, but unless we can measure our own organisms, how can we know what effect these processes are having?'

(Photograph omitted)