Kielder is home to about 70% of England's red squirrel population

Red squirrels in other parts of the country are facing potential extinction due to the squirrel pox virus which is relatively harmless to greys.

Kielder Forest is home to about 70% of England's red squirrel population.

Researchers have found the dense conifers make it difficult for greys to penetrate and pass on the virus.

The squirrel pox virus poses one of the biggest challenges to the creature's continued existence in England, the Forestry Commission said.

Fighting chance

For the past three years the commission, Newcastle University and Queen Mary, University of London supported by Mammals Trust UK, have worked on a pioneering project in Kielder Forest as part of a wider initiative to conserve the species in northern England.

Researchers have looked at the likely impact of the disease when greys arrive in significant numbers at the edges of the forest from Scotland and northern England within the next five to 10 years.

While infectious grey squirrels are likely to cause localised extinctions of reds in Kielder, this should not irrevocably affect the core population and numbers should recover.

The main reason is that red squirrels succumb to the pox virus rapidly and any squirrels that become infected at the edge of Kielder are unlikely to transmit the disease to the core population and the disease burns out.

Bill Burlton, from the Forestry Commission, said: "This research breaks new ground.

"Squirrel pox has always been a shadow hanging over our efforts to improve the habitat for reds, so we are pleased that at least in Kielder the models indicate we have a fighting chance of keeping a viable population."