David Collins had applied for listed building consent to install a through-floor lift at Adsdean House, northwest of Chichester, a Grade II listed property previously home to Lord Mountbatten.
But his plans have been blocked at appeal, after being rejected by the South Downs National Park Authority in September last year.
Planning Inspector B Philips concluded that the proposed works would “fail to preserve the special architectural and historic interest of the Grade II listed building” and would result in “harm to its significance”.
The property, located on Adsdean Park Road, near the village of Funtington, was built in 1850 and later extended by architect Norman Shaw in 1877.
It is most memorable as the former residence of Lord Mountbatten, uncle of Prince Philip and the first governor general of independent India.
The proposed lift would have connected the ground and first floors, with the base situated in a modern cupboard and the shaft passing through a lath and plaster ceiling and softwood floorboards.
A planning application on behalf of Mr Collins, who is a steward of the National Trust, suggested the proposal would be “easily reversible”.
Mr Collins has previously opened the property to private groups and visitors, including members of the Mountbatten family and families of former staff and servants.
The application had argued that the scheme would only affect a small section of lath and plaster dating from around 1900, and that it would provide public benefit by allowing continued access and interpretation of the house.
But the planning inspector said that although the level of harm was “low,” it should still be given “considerable importance and weight”.
The inspector acknowledged the public value of open house activities but gave them only “modest weight,” noting that the tours and events are conducted on an informal, ad hoc basis, with no guarantee of continuation.
“On balance, in giving considerable importance and weight to the harm to the significance of this designated heritage asset, I find that this would not be outweighed by the public benefits that the proposal would generate,” they said.
