King Charles tells Britain to weather the cost of living crisis whilst wearing a hat worth 5 billion pounds.
(thespectaclemag.substack.com)
My understanding has been that the Crown Jewels are held in trust for the State by The Crown/The Firm, and have been for centuries. That was set up specifically by the court to stop King Humphry Wonderblumph or whichever from selling them for booze money (and so the king he could borrow against the national trust when needed funds from the barons) - so no the king can't sell the crown jewels without the consent of (now the modern parliment, then the court/feudal parliment).