SSSI - Site of Special Scientific Interest
Latest: The new Countryside and Rights of Way Act 2000 has made some significant changes to SSSI legislation in England and Wales.
Under the Wildlife and Countryside Act 1981 (amended 1985) the government has a duty to notify as an SSSI any land which in its opinion is of special interest by reason of any of its flora, fauna, geological or physiographical features. In Northern Ireland some areas are designated as Areas Of Special Scientific Interest under the Nature Conservation and Amenity Lands (Northern Ireland) Order 1985, but as this is essentially the same thing (although there are some important differences), this page is mostly relevant to both designations.
SSSIs are designated by English Nature, Scottish Natural Heritage, Countryside Council for Wales, or DoENI. This body is known as the designating body. An SSSI is not necessarily owned by a conservation organisation or by the Government - in fact, they can be owned by anybody. The designation is primarily to identify those areas worthy of preservation. An SSSI is given certain protection against damaging operations, and any such operations must in theory be authorised by the designating body. There is a list of just what can and cannot be done on an SSSI. The status also affords a certain amount of planning protection, but in practice this is sometimes not sufficient to prevent development.
The Countryside and Rights of Way Act 2000 strengthened the law giving greater power to the designating body to enter into management agreements, to refuse consent for damaging operations, and to take action where damage is being caused through neglect or inappropriate management. Local Authorities and other public institutions now also have a statutory duty to further the conservation and enhancement of SSSIs both in carrying out their operations, and in exercising their decision making functions, which includes planning decisions.
SSSIs form the basic unit of UK protected area legislation - most higher designations are superimposed (sometimes a little loosely) onto existing SSSIs.

Essex Wildlife Trust, Abbotts Hall Farm, Gt Wigborough, Colchester, Essex CO5 7RZ