The Government will propose what amounts to an almost total ban on damaging development in some of Europe's rarest, most valuable habitats with which Britain is well endowed.
For the first time, several dozen offshore sites with rich collections of fish, shellfish and marine plants will also receive a measure of legal protection, the Department of the Environment will announce.
These moves represent Britain's implementation of the EC Habitats Directive, aimed at protecting the continent's most threatened species and habitats with a network of protected and managed Euro- reserves.
Sites receiving extra protection will include parts of the blanket bog in the flow country of Scotland, the raised peat bogs of England - already damaged by commercial peat extraction - dunes, salt marshes, and the lowland heaths of southern England.
But when the Department of the Environment reveals its plans in a consultation paper tomorrow, environmental groups are likely to protest that the Government is missing a huge opportunity to put wildlife conservation on an even stronger footing.
The Government does not want to impose draconian restrictions on the private landlords who own many of the key wildlife sites. Many are Tory supporters. Environment ministers speak of 'working with the grain' of local rural communities, seeking to encourage rather than compel landlords, tenant farmers and crofters to manage their land in ways which favour the threatened plants and animals.
For the first time, however, a government duty to prevent destructive development on the wildlife sites it nominates will be enshrined in law.
There is no such duty at the moment and between 200 and 300 of the existing government-designated wildlife areas - unimaginatively titled Sites of Special Scientific Interest (SSSIs) - are damaged or destroyed each year.
Conservation groups would like the majority of Britain's existing 5,500 SSSIs to be covered by the new Habitats Directive. But the Government is expected to designate only a few hundred as European Special Areas for Conservation.
Carole Hatton, planning officer for the World Wide Fund for Nature, said Town Common near Christchurch was the kind of site urgently needing protection through the European directive.
The favoured route for the planned Christchurch Relief Road goes through the common, which is home to endangered reptiles and already an SSSI. However, the Government will not announce its list of Euro-sites until next year.
'Ministers may just about follow the letter of the directive, but they're not following the spirit,' said Ms Hatton.