A deadly squirrel disease which only affects reds could see the species disappear from some of its last remaining English strongholds within a decade, new research revealed yesterday.
Previously scientists believed that grey squirrels were wiping out native reds simply by taking over their habitats, but an international study has blamed a virus which they transmit to the red population, killing them within a fortnight.
Researchers have now called for a selective cull of greys in "gateways" to red squirrel areas to prevent the protected species from being exposed to the virus.
According to scientists from Newcastle University and London's Queen Mary University, the disease, squirrel poxvirus, threatens to wipe out red squirrels in some of the areas in which they remain in northern England within ten years.
In areas where it has been detected, the rate of decline in reds is 17 to 25 times higher than in places where there has been no outbreak.
Red squirrels have been in Britain for the last 10,000 years and are protected under the UK's Wildlife and Countryside Act, while domineering greys were introduced from the United States more than 100 years ago.
Researchers say that in the absence of a vaccine, the only effective way of stopping the spread is to target greys at the narrow entry points and corridors to England's 16 designated red squirrel refuges, by killing the small numbers of greys that may come in.
Squirrel poxvirus was probably brought into the country with some of the American greys, of which 70 per cent have been exposed and are carriers.
While they appear to escape unharmed, it is fatal to reds, causing sores and ulcers on the face, feet and thighs.
Yesterday's recommendations for grey squirrel management appear in two academic journals, Epidemiology And Infection, and Biological Conservation. Scientists studied Cumbria and Norfolk, where the virus had broken out, and compared them with Scotland and Italy, where there was no trace of the disease, and found the reds' population area decline was up to 25 times worse where they were exposed to the disease.
A selective, small-scale cull of grey squirrels has been achieved in Kielder Forest, Northumberland, after experts analysed the red squirrel refuge and identified four areas through which greys could get access.
There are now plans to apply the approach to the other 15 squirrel refuges in Cumbria, Northumberland, North Yorkshire and Merseyside.
Dr Peter Lurz, a research associate at the Institute for Research on Environment and Sustainability at Newcastle University, said: "It is vital we get this disease under control, especially as it is now threatening to spread across the border to Scotland with severe consequences for red squirrel conservation there.
"We are not trying to wipe out the grey squirrel but as conservationists we have a duty to look after the red squirrel as it is a protected, native species.
"It's a practical and affordable solution."
Tony Sainsbury, who is a lecturer in wild animal health at the Zoological Society of London, added: "The cases seen by ZSL's national red squirrel disease surveillance programme clearly demonstrate the severity and debilitating nature of the squirrel poxvirus disease on red squirrels."