Campaigners were celebrating today as the Government signed into existence the new South Downs National Park - and announced it would be bigger than previously planned.

Environment Secretary Hilary Benn, on a visit to Ditchling in East Sussex, said the Park's provisional boundary would be stretched to encompass a number of additional areas following lobbying by residents and conservationists.

The 632-square mile protected area, from Beachy Head in East Sussex to the edge of Winchester in Hampshire, will now include land at Green Ridge in Brighton and Hove, the A27 embankments, land behind Roedean Crescent, Patcham Recreation Ground, land at Plumpton, Castle Goring, Gote farm, and the boundary at Offham.

A new South Downs National Park Authority, charged with conserving and enhancing the Park's natural beauty, wildlife and cultural heritage and helping improve public enjoyment of the area, is expected to be established by April 2010 and become fully operational a year later.

Signing the official order to designate the South Downs as England's ninth National Park, home to an estimated 120,000 people, Mr Benn said: "The unique chalk downlands and heavy weald clay landscapes which make up this wonderful countryside will now be protected for everyone to enjoy. National Park status will attract new visitors to the South Downs and bring investment into the local area."