Prickly, stinging weeds such as nettles and brambles may be pursued to destruction by gardeners, but farmers' increasing tolerance of such plants has provided a lifeline for endangered British wildlife.

Dormice are among the creatures most likely to welcome the increased abundance of blackberries, and stinging nettles are a valuable source of food for the caterpillars of red admiral and peacock butterflies.

Stinging nettles, hawthorn and brambles have thrived since 1998, rising to become the fourth, fifth and seventh most abundant plants in Britain as farmers manage the countryside less rigidly through schemes such as set-aside and the conversion of arable fields to grassland.

Hedgehogs are afforded more cover from predators by the rampant growth of “big weeds” on British farmland over the past decade, and birds including linnets and stone curlews benefit from the increase in seed-bearing plants.

However, the flourishing plant growth identified by the Countryside Survey 2007 report, published yesterday, is not such good news for other plants: the unchecked growth of such shrubs has caused a problem for several other wild plants, especially the smaller, lower growing varieties.

Peter Carey, of the Centre for Ecology and Hydrology, the report's lead author, said that wild strawberries and harebell were among the species being overgrown by nettles and brambles. “The stinging nettles are the sort of plant we don't want too much of,” he said. “They tend to swamp other vegetation. The countryside has got taller and a lot less managed.”

The rest of the top ten was taken up by grasses, with rye grass identified as the most abundant, followed by Yorkshire fog and false oat. Heather, which a decade ago was the seventh most abundant, fell to eleventh place. Dr Carey added: “The overriding message from the 2007 results is that previous intensive management of the countryside has relaxed over the past 30 years and particularly during the nine years since the last survey.”

Black bryony, wood avens and ivy lead the table of plants that have become more widespread, while broad-leaved willowherb, oblong-leaved sundew and marsh foxtail can now be seen in fewer places.

The number of species of plant found on arable land rose by 30 per cent from 1998 to 2007, illustrating the increased willingness of farmers to tolerate weeds among their crops.

The trend towards letting the countryside run wild is now in doubt, however, because the EU's set-aside scheme, which conservationists have regarded as being especially beneficial to birds, has been scrapped.

Despite the success of some common plants in open countryside the report identified some areas of concern, particularly the condition of ponds. The survey, which assessed conditions and species levels in 591 plots measuring a square kilometre selected at random in England, Wales and Scotland, found that 80 per cent of ponds in England and Wales were in poor condition and that there had been a 20 per cent loss of species diversity.

It also found that the range of plants found alongside streams fell by 8 per cent from 1998 to 2007. Pollution caused by fertilisers washing off fields into streams was one of the factors blamed. Hedgerows were a further concern, with 6 per cent of managed hedges in the countryside being lost. However, the area of broadleaf woodland increased by 6.9 per cent.

The £10million survey, the biggest of its kind, was commissioned by the Department for Environment, Food and Rural Affairs and the Natural Environment Research Council. It was the fifth since 1978.

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