Action to safeguard one of Britain's fastest-declining mammals has resulted in a 300 per cent increase in the animals' population.

The boost in water vole numbers has taken place in Sussex after a three-year partnership.

The number of water voles has risen in the county from just 100 to 342, following work on their waterside habitats.

In the UK, the population of the water vole - immortalised as Ratty in Wind in the Willows - has declined by 88 per cent in only seven years between 1990 and 1997.

In Sussex, populations were harder-hit, falling by 97 per cent. Experts predicted local extinction by 2003.

But a conservation initiative between the Environment Agency, the Chichester Sustainable Farming Partnership, WildCru (Oxford University's Wildlife Research Unit) and the Farming and Wildlife Advisory Group has rescued them.

The project also included important contributions from landowners, West Sussex County Council and Sussex Wildlife Trust.

It created about 40 miles of 18-ft high grass margins along watercourses so the voles can make their homes and thrive.

This approach has also improved habitats for a variety of other creatures, in particular brown hares, farmland birds and insects.

Paul Smith of the Environment Agency's fisheries, recreation and biodiversity team said: "Due to the plight of water voles facing extinction, we had to take conservation action in the Sussex area.

"Water vole populations were hit hard as a result of intensive farming and changes to water courses, where the voles make their habitats, which had suffered from heavy engineering work for flood defence and land drainage purposes.

"Predators such as mink were also a major factor in the decline of the water vole in the county.

"We are delighted that by working with our partners, we have seen a large increase in local water vole populations."

New initiatives to deal with similar issues are starting with the Upper Thames and Rye Levels.