Organic farming is increasingly the saviour of Britain's rare wildlife, the Government's top conservation adviser said yesterday.

Many species of flowers, insects and birds that are declining on modern conventional farms prosper on organic ones, said the chief executive of English Nature, David Arnold-Forster.

Sound scientific research now shows that birds such as skylarks, song thrushes and swallows, formerly common flowers such as buttercups, and many types of smaller organisms such as insects, spiders and earthworms do "overwhelmingly better" in an organic environment, Mr Arnold-Forster told the national conference of the Soil Association, the organic farming campaign group.

His comments will be seen as independent support for the Soil Association's own claims about the wildlife benefits of "going organic".

Although argument may continue to rage about whether organic food is good for you, there is little doubt that the farming system that produces it is good for biodiversity.

The Soil Association offered detailed evidence in a report  last year that the organic system, in which chemical fertilisers and pesticides are replaced as far as possible by natural equivalents, supports much higher levels of wildlife than "agribusiness" does.

Mr Arnold-Forster confirmed this, saying that English Nature had reassessed organic farming's wildlife benefits. "The conclusions of our work, reviewing extensively literature and experiments, are that there are higher numbers and greater densities of wildlife on organic farms and there is a greater diversity of wildlife on organic farms.

"Overwhelmingly, whether it is birds of conservation concern, [declining] weed species or butterflies, the wildlife species which have suffered the greatest declines on farmland as a whole over the last 50 years do better under an organic farming system."

Mr Arnold-Foster said that pairs of organic and conventional farms had been compared for diversity in trials carried out across Britain over the past 10 years. Tests in the Chilterns showed there were greater numbers of 18 species of flowers on organic farms, while 13 species were found exclusively on the more specialist farms.

Other trials showed that the buttercup – the most rapidly declining wildflower on any British farm – was only present in organic fields, Mr Arnold-Foster said. Earthworms, birds and spiders were also more abundant in an organic environment.

In a survey of 92 species examined over four years, 30 were found to be more common on organic farms compared with only four found in high numbers on conventional farms. "This is sound science," Mr Arnold-Forster said. "These benefits can help us achieve our fundamental mission of conservation and wildlife gain."

The benefits of organic farms included the limitation of pesticides, the encouragement of greater crop diversity, which would in turn attract birds such as skylarks, and reduced demand for water.

The Environment minister Michael Meacher said theGovernment planned to encourage farmers to be greener. "Agricultural practices are one of the most important influences on wildlife in this country," he said.