JOIN USThe First-Tier Tribunal on information rights said Thursday that Charles' 136,000-acre (55,000-hectare) estate - the Duchy of Cornwall -- must abide by some of the same regulations followed by other government bodies.
The ruling stems from a demand for information made by environmental activist Michael Bruton, who was concerned over the Duchy's oyster farming plans in Port Navas, a protected area of salt meadows and mudflats about 300 miles (480 kilometres) southwest of London.
The prince had argued that the estate is effectively a private inheritance and should be exempt from disclosing the information.
Judge John Angel acknowledged that the estate had a "historical context which is complicated and possibly unique" but ruled that it was a public authority for the purpose of environmental information regulations, which work like freedom of information laws for environmental issues.
Prince Charles' office said it was still considering whether to appeal the judgment. Bruton could not immediately be reached for comment and there was no immediate response from his group, Port Navas Quay Preservation.
The Duchy of Cornwall was created in 1337 by Edward III for his son and heir, Prince Edward, in a bid to provide him and future heirs to the throne an income from its assets.
The land is broken up over 23 counties and includes residential and business properties besides agricultural tracts. The largest chunk is in Dartmoor, in southwest England, where farmers rear cattle and sheep.
It also includes the Isles of Scilly, just off the coast, which are known for their flower farming.
The duchy earned Charles almost 18 million pounds (USD 29 million) last year. The bulk of the money is used to fund the prince's travels and his charity work; the rest is for Charles to keep.