We said in a section at the end of this article entitled Collapsing colonies that cases of entire bee colonies dying out suddenly had been reported in the UK. The Department for Environment, Food and Rural Affairs would like to make clear that fears that colony collapse disorder had struck in the UK have so far proved to be unfounded.

Let the neighbours mutter in dismay. Unruly, overgrown gardens have been highlighted as a vital refuge for the nation's dwindling bumblebee population, in a countrywide survey by conservationists.

Patches of garden that are left to run wild have been ranked as one of the richest for nesting bumblebees, offering better shelter and food resources than farmland and wooded areas, the report finds.

More than 700 volunteers took part in the National Bumblebee Nest Survey, with each scouring a garden and at least one other natural habitat to help with the understanding of the insects' favoured nesting sites.

Britain has about 25 native species of bumblebee, although three have been declared nationally extinct. Populations of nine other species are so precarious they have, or are due to be, designated special concerns by the government's Biodiversity Action Plan. In total, 15 species have seen serious contractions in their numbers, a drop that has alarmed conservationists.

The survey, published today in the Journal of Applied Ecology, found that gardens had among the highest densities of bumblebee nests, with an average of 36 nests per hectare.

Farmland fencing was also identified as a rich habitat for the insects, with 37.2 nests per hectare. Other countryside habitats made less suitable nesting grounds, with hedgerows being home to about 30 nests an hectare and woodlands just 11 nests an hectare.

Bumblebees build nests above ground or just beneath and line them with moss and leaves. Slightly neglected gardens are particularly good habitats for the bees because of the abundance of nesting options, such as compost heaps and bird boxes, and additionally the rich variety of flowers over the year that many gardeners cultivate.

"These kinds of gardens really provide a refuge for bumblebees, as long as people don't manage them too carefully," said Juliet Osborne, an ecologist at Rothamsted Research, the agricultural research centre based at Harpenden, Hertfordshire. "If you've got different grass areas, flower beds, compost heaps and hedges, there's a vast variety of habitats for bumblebees," she said.

Dr Osborne added: "Bumblebees are happier in gardens that are not perfectly tended. If you can leave some of the grass uncut, and a few areas looking slightly untidy, that's what they love. Even if most of your garden is neat and tidy it's a good idea to let some areas stay undisturbed. Behind the garden shed or garage are good places. You should also make sure you've got a variety of plants that flourish throughout the season."

Bumblebees are important pollinators of crops and wild plants, but their populations have been in steep decline for the past 50 years. The loss is thought to be linked to the impact of intensive farming on the plants the bees seek out for food. But as well as food, the insects need nesting sites for queens to start new colonies every spring.

Analysis of the survey data showed that in springtime queens favoured nesting sites tucked into the straight-running lines of fences that border green spaces. Although gardens account for only 2% of the land in Britain, the high density of fences and borders that mark out adjoining gardens makes these individual plots rich nesting sites for bumblebees. "The gardens seem to be where the bumblebees establish themselves before moving out to the countryside," said Dr Osborne.

Changes in farming practice since the second world war have seen the size of fields increase, which has led to fewer hedgerows, making the managed countryside a less attractive prospect for the insects. In the open countryside, bumblebees may have to expend more energy foraging for nectar because wild flowering plants will be seasonal and possibly sparsely distributed.

That gardens have been found to play such a critical role has added to scientists' concerns about the trend for paving over lawns. "This is a very serious issue for the bumblebees," Dr Osborne said.

In April, a report from the Royal Commission on Environmental Pollution concluded that the loss of garden greenery - to patios, decking and parking space - was having a devastating effect on wildlife in Britain. In urban environments, with few trees, shrubs and grass, many creatures find it impossible to find food and shelter, it said.

Dr Osborne said the latest study highlighted habitats, such as woodland borders and farmland fences, where conservation efforts should be directed. "Although in the countryside the total area occupied by field margins and hedgerows is relatively small, sympathetic management - as encouraged by environmental stewardship schemes - could improve bumblebee nesting opportunities in farmland."

Explainer: Collapsing colonies

The rapid decline in bee populations over the past 50 years in the UK is generally blamed on intensive management of farmland, which has led to a loss of hedgerows and flowering plants that are crucial for the survival of the insects.

But recently, there has been an increase in reports of entire bee colonies dying out suddenly, a phenomenon called "colony collapse disorder". Such sudden deaths are usually witnessed late in the summer or early spring when older bees die off, leaving the queen and workers unprepared to forage.

The US was particularly badly hit, with beekeepers in 24 states reporting such cases. Other incidents followed in Italy, Spain, and Portugal, as well as in Britain.

In April, a team of scientists at Landau University in Germany suggested tentatively that radiation from cell phones might be to blame for the collapse of colonies by interferring with the bees' navigation systems. They put phone base units into two honeybee hives and timed how long it took the animals to return after being released 800 metres away. After 45 minutes one of the colonies had still not returned. The lead researcher, Jochen Kuhn, said the study provided only a "hint" at a cause, and did not prove that radiation from the phone units was to blame.