But it is crown land when it suits them, and private land when it does not.
The Duchies of Lancaster and Cornwall have remained independent of the Crown Estate. The revenues go to the Monarch and his eldest son respectively.
But they can not sell them.
The Duchy of Cornwall automatically owns all mines in Cornwall, irrespective of the individual ownership of the land. This includes mines under the sea extending beyond Cornwall but originating there.
It has the right to mine underneath privately owned homes without the consent of the owners.
The Duchy owns any ship wrecked on Cornish shores which is not claimed within 1 year.
The Duchy owns about two thirds of the foreshore (tidal land and riverbeds) in Cornwall and the Isles of Scilly, although parts of this land have been sold.
The Duke has the exclusive right to the carcass of any whale or sturgeon washed up on Cornish shores.
The Duchy of Cornwall has the right to claim “Bona Vacantia” within Cornwall. That is to say, where property within Cornwall becomes ownerless, it belongs to the Duke of Cornwall instead of the government. Typically this would arise where a person dies without leaving a will and without having any traceable relatives. The Duke also administers the estates of people who die without a will, even if the rightful owner is eventually traced.
The Duke owns “treasure troves” in Cornwall: finds of buried valuable metalwork of a certain age. It has only enjoyed this right in law since 1996.
Special provisions and exemptions allow the Duchy to commit any act under the following laws which would be a crime for anyone else:
The Wildlife and Countryside Act 1981
Water Industry Act 1991
Countryside & Rights of Way Act 2000.
Land Reform (Scotland) Act 2015.
In 1967, long-term leaseholders in England and Wales acquired the right to have those leases extended automatically, whether the landlord agreed or not, albeit on payment of compensation. This added enormous value to long-term leases and security to hold property down the generations.
This does not apply to the Duchy of Cornwall.
And more here
www.republic.org.uk/the_duchy_s_powers_and_privileges