A massive cull of grey squirrels is to take place across England to try to halt declining numbers of the endangered native red population.
Native red squirrels are outnumbered by greys by 66 to one
Biodiversity minister Jim Knight said "humane and targeted pest control" would cull greys in areas where red squirrels are being 'squeezed out'.
Most UK reds are confined to Scotland, Cumbria, Northumbria, the Isle of Wight and islands in Poole Harbour.
They are weaker than grey squirrels, which also carry the squirrelpox virus.
Mr Knight said the aim was not to completely eradicate the greys, which have a population estimated at more than two million - outnumbering red squirrels by 66 to one.
But he said: "We must control them effectively now or there will be serious consequences."
Grey squirrels were introduced to Britain from North America in the 19th Century and have thrived in lowland areas.
It is thought the cull will use poison to reduce numbers over the next three years.
The cull is being jointly organised by the Department for the Environment, Food and Rural Affairs (Defra) and the Forestry Commission, after consultation with various groups, including English Nature, the National Trust, the RSPCA and the European Squirrel Initiative.
The policy is currently aimed only at England. Scotland and Wales have devolved powers in this area; although the perceived scale of the grey squirrel problem means groups in Scotland and Wales were fully consulted in drawing up the policy.
Mr Knight added: "Many people love grey squirrels, but the reality is that they are a real problem for some of our most threatened native species.
"Grey squirrels seriously threaten woodland management through damage to trees and woodlands and by squeezing out red squirrels and possibly other wildlife like woodland birds."
He said projects such as Red Alert north England, which manages woodland areas so they are less well-suited to grey squirrels, illustrated that intervention could work.
Lord Clark, chairman of the Forestry Commission, said the policy gave workers a "clear mandate" for protecting native species of woodland and wildlife, while allowing a "controlled presence of non-native species".
But the European Squirrel Initiative, which campaigns for the protection of the red squirrel, called for more effective ways of controlling the grey population.
It said drugs should be considered to sterilise the greys.