Actor Brian Blessed saw 100 walkers set off on a nine-mile hike to protest at new boundaries proposed for the South Downs National Park.
Brian Blessed addressed the 100 walkers as they set off
Mr Blessed spoke to walkers at Harting Down, West Sussex on his last event before he steps down as president of the Council for National Parks.
Sunday's walk coincides with the 60th anniversary of the South Downs first being proposed as a National Park.
Campaigners want the Low Weald reinstated into the proposed park.
'Digest and respond'
A revised map of the proposed boundaries published on Monday by the government leaves out Liss and Petersfield in Hampshire, and Midhurst and Petworth in West Sussex.
An inspector who heard evidence at the public inquiry, which ended in March 2005, also proposed excluding Lewes, Steyning, Arundel and Ditchling in Sussex.
A public consultation runs until 13 August.
"We are delighted that the inspector has recommended that the South Downs should become England's 10th National Park," said Kate Ashbrook, chairman of the council.
"However, six weeks is not long enough to digest and respond to this important consultation.
"Given the radical proposals to exclude a large chunk of the Low Weald in Hampshire and West Sussex there needs to be more time.
"Such a radical reduction would be a missed opportunity to protect this beautiful countryside for future generations."