A unique historic landscape that has survived intact for 1,000 years will be lost to developers unless the Government honours a promise to make it part of Britain's newest national park, conservationists warned.

The Western Weald in West Sussex is one of the last remaining areas in the country to have retained field patterns from the early Medieval period. It is also home to the rarest bat in Europe as well as swathes of ancient woodland and a range of endangered birds and butterflies.