'Historic day' for South Downs National Park
Campaigners have welcomed a "historic day" as the South Downs National Park Authority comes into full operation.
The authority has taken on its legal powers and will be responsible for all planning within the park.
The park, which covers 627 square miles across Sussex and Hampshire, was approved on 31 March 2009 and was officially designated a year later.
It is more than a decade since the government announced its intention to designate the area as a National Park.
Robert Cheesman, who chairs the South Downs Society, said he was looking forward to helping the authority protect a "very special part of Britain".
The park stretches from Winchester in Hampshire to Eastbourne in East Sussex, and includes woodland, heathland, downlands and the white chalk cliffs at Beachy Head.
The new park authority expects to deal with about 4,000 planning applications a year.
Fifteen local authorities will carry out many of the day-to-day planning services, but the park authority will retain overall control.
Margaret Paren, who chairs the authority, said: "This is be a long-awaited and historic day for everyone who loves the South Downs."
Supporters will be taking part in a celebratory five-mile walk from East Dean to Birling Gap, near Eastbourne from 1015 BST.