Ralph Percy, the 12th Duke of Northumberland and a friend of the King, planned to rip up 37 plots on his family estate Syon Park in Isleworth, west London, to build 80 flats.

After an eight-year battle, which has involved two public inquiries, the planning inspectorate has rejected an appeal by Northumberland Estates, the duke’s company, and Park Road Allotments remain protected.

The three-acre site has been used as allotments since 1917 when the land was leased to the council by one of the duke’s ancestors to feed wounded soldiers returning from the First World War.

The duke, 67, who has an estimated family fortune of £445 million, had a proposal for the flats rejected by Hounslow council in 2021 after a public campaign, which included a thousand letters from locals objecting to the plans and public protests outside the duke’s neighbouring Syon House.

Following an appeal, the inspectorate concluded that building on the land would harm protected local open space and heritage assets and restrict allotment provision when demand in the area is high.

Colin Barnes, planning and development director at Northumberland Estates, told The Times: “We are disappointed that this scheme which would have provided much-need affordable housing while retaining green space and allotments has not been approved. We will take some time to consider our options.”