Protesters turned out in force at the site of the proposed Horncroft sandpit near Fittleworth, after hearing that their MP was due to visit.
Nick Herbert, whose Arundel and South Downs constituency now includes Fittleworth, had arranged to meet representatives of parish councils which have lined up to oppose the scheme.
He found a big gathering of local people wanting to stress their worries about the Barlavington Estate's application, which has been submitted to West Sussex County Council.
Mr Herbert, the former shadow environment secretary, is the minister of state for policing and criminal justice in the coalition government.
Before the election he formally objected to the sandpit proposal in a letter to the county council.
The MP said after his Horncroft visit: "I asked if I could meet the parish council chairmen and some of the local people concerned about this issue.
"But word got around in just four days and hundreds of people turned out to show their support. This just shows the depth of concern about what I think would be a very damaging proposal."
Sir Sebastian Anstruther's Barlavington Estate is seeking consent to extract 1.5 million tonnes of sand from the 54-acre site at Horncroft Common over the next 20 years.
As well as local objections, on grounds of environmental impact in the new South Downs National Park, loss of wildlife habitats, and lorry traffic, the proposal has also drawn opposition from the South Downs Joint Committee, the Woodland Trust, the Campaign for National Parks, the South Downs Society and the Campaign to Protect Rural England.
Objectors claim government policy rules out quarrying in national parks except in exceptional circumstances, which they say do not exist.
Mr Herbert declared the sandpit would be 'totally inapproriate' in a national park which should be receiving the highest level of protection.
He encouraged them to write to him at the House of Commons so he can forward their concerns to the county council.