Ask the man in the street what he knows about Porton Down and most will talk about germs, warfare and diseases.

But there is more to this top secret Wiltshire establishment than first meets the eye.

Few people realise that in the middle of this potentially deadly operation is a unique nature reserve where threatened species are winning the fight for survival.

Among them is the Stone Curlew one of this country's most shy and rarest birds which is successfully breeding on part of Porton Down's 7,000 acre test range

Almost half of this chalk downland which is run on Salisbury Plain by the Defence Science and Technology Laboratory, is in fact a designated Site of Special Scientific Interest because it has unique flora, fauna and landscape.

The Stone Curlew success story is particularly important because it is estimated that there are only 270 breeding pairs left in the UK and up to 20 per cent of them are on the Plain.

Because of the work it does, the Porton Down range has been left untouched by modern farming methods, providing ideal conditions for this once common farmland bird.

The site has its own conservation group, and is assisted in its work by national and local conservation bodies.

Schools, natural history societies and other groups regularly visit the SSSI.