Colin Sykes reports: "Numbers now in dramatic decline"

Dr Simon Lyster, director general of The Wildlife Trusts, says England will lose its native red squirrel by 2010 and the rest of the UK may not be far behind, unless the drastic measure is taken.

Dr Simon Lyster's dire warning

He told BBC Radio 4's Today programme: "Unfortunately we really have no choice in the short-term."

The organisation has produced a report "Red or Dead" to warn about the problem.

"The situation in mainland England is looking very, very dire," said Dr Lyster.

The main culprit is the invader which was introduced to the UK at the end of the last century.

Invader: The grey squirrel is a better survivor

"The grey squirrel is basically the problem.

"We've got to find ways of excluding grey squirrels from red squirrel areas and in the short-term that is going to mean controlling grey squirrels."

He explained "that means killing them", but insisted that this was only necessary "in the areas where they interface with reds".

"Nobody's suggesting doing it all around England," he said, perhaps forgetting Viscount Brookborough who in June suggested to the House of Lords a "shoot on sight" policy.

The government rejected this plan, with minister Baroness Farrington fearing letters from parents who "get enormous pleasure taking their children to feed grey squirrels".

Dr Lyster admitted he was uneasy about killing one species to save another but believed it was the right thing to do since the red had been in the UK for 10,000 years.

Survival of the fittest

Popular myth suggests that the grey wins the battle for survival by force but violence is not the secret of its success.

It simply makes more efficient use of available food, produces more offspring and is generally more robust than its cousin.

It may also carry a virus which kills the red.

Dr Lyster said experience in areas where the red variety was surviving showed "controlling" greys was not the only solution.

Less serious action could also be successful, such as introducing "buffer zones" of pine trees or barren land to stop the grey invasion.

Once greys become established, reds can be expected to die out in just 15 years.