The duchy’s powers go even further.

Prince Charles inherits the possessions of anyone who dies in Cornwall without a will or next of kin, a power that in some years has yielded hundreds of thousands of pounds. He funnels the money into charities after deducting his costs.

The duchy owns the right to mine in Cornwall, even under private homes — a right that it registered to extend as recently as eight years ago.

Most extraordinarily in critics’ eyes, the duchy has the right to be consulted on any legislation that affects its interests. Over the years, governments have interpreted that to include bills about hunting, road safety, children’s rights, marine access and wreck removal. A 2008 planning law exempts the duchy from ever committing a planning offense.

A similar carve-out gives Prince Charles unusual power over some homeowners on the Isles of Scilly, a picturesque archipelago off the southwestern coast of England, and in Newton St. Loe, a village near Bath.

People like Mr. Davis own their homes there, but the duchy owns the ground on which they are built. Such an arrangement is not uncommon in England, but homeowners would usually have the option to buy the land. Not on some duchy land.

That enables the duchy to charge small ground rents to homeowners grandfathered into long leases, like Mr. Davis. Once those leases lapse, it can also raise rents to thousands of pounds per year, making it difficult for people to sell or mortgage their homes.

In one case, a couple built a house on the Isles of Scilly, only to have the duchy force them to sign a lease bequeathing the property to Prince Charles’s estate upon their death, said Lord Berkeley, a Labour peer in the House of Lords.