Proposals to give the 116km stretch of chalk hills the same status as the Lake District and Snowdonia have been backed by bodies including the Countryside Agency and the Council for National Parks.
The Countryside Agency, leading the case in favour of the designation, told the inquiry that the South Downs meets the statutory criteria for national park status. Senior countryside adviser David Thompson argued that the downs are an "exceptional recreational resource of national importance".
Thompson rejected arguments that the downs should not be designated because the area is not as remote as other parks, noting that Sir Arthur Hobhouse's original vision for national parks stated that it would be wrong to exclude less rugged areas. He told the inquiry that the South Downs offer "a sense of relative wilderness" and open-air recreation of national park quality.
Designation opponents include East and West Sussex County Councils, which are set to lose planning powers if the park is created. West Sussex County Council leader Henry Smith said that planning decisions are best made by elected representatives who can be held "fully accountable", rather than Whitehall appointees.
The National Farmers Union is also opposing the designation. A spokeswoman said: "We would prefer a green farming scheme to enhance the South Downs."