The endangered water vole is making a comeback in parts of the UK, according to a survey which revealed dozens of "hotspots" for the animal immortalised as Ratty in Wind In The Willows.

But the river-bank dwelling vole, which saw numbers plummet by 90 per cent, is still struggling in many areas and there is "a long way to go" before populations return to healthy levels, the Environment Agency said.

The water vole saw numbers crash in the face of predation by invasive mink, which established themselves in the countryside after escaping from fur farms, and the loss of river-bank habitat.

The mammals were given full legal protection two years ago, making it a crime to intentionally kill or injure a water vole or disturb their habitats, in a bid to protect them.

Data gathered from 36,000 individual water vole surveys across the UK identified more than 30 "hotspot" sites for the mammal - from grazing marshes and ditches in Yorkshire to Pennine moorlands and east coast wetlands.

At some sites, including the Somerset Levels, mink control and habitat creation saw a dramatic improvement in their fortunes, while other areas such as uplands where there has been little development have remained strongholds.

In Wales, important sites were identified in the Wye Valley, on the Isle of Anglesey, in Snowdonia, Denbighshire, Ceridigion and Llanelli, while in Scotland, upland areas, including the Cairngorms, are home to extensive populations, the Environment Agency said.

But the data, which is being used to map populations of water voles across the UK, also shows how badly the animal is faring in some parts of the country.

Water voles are extinct in Cornwall, and there are just two, very small populations remaining in Devon, while in much of the south east of England and south and west Wales they are continuing to decline.

In addition to efforts to control mink and ensure the voles have suitable river-side habitat, conservation groups have also been breeding and releasing water voles into areas where they have been in decline.

Alastair Driver, the Environment Agency's national conservation manager and chairman of the UK water vole steering group, said: "Water voles are doing really well in some areas where widespread long-term mink control has been combined with habitat creation, but it is clear that there is still a long way to go before water vole numbers return to healthy levels.

"The Wildlife Trusts are now working hard for us by using this fantastic dataset to produce maps showing where all the hotspots for water voles are around the country so that they can be protected and encouraged to spread further afield."

The Environment Agency said improvements to water quality over the past two decades also helped wildlife including water voles, otters and salmon, return to many rivers.

Mr Driver said the agency had plans to revitalise more than 9,000 miles of rivers in England and Wales by 2015 which he said would contribute to ensuring the survival of water voles in the UK.