Could Payment Be Deferred Until an Asset Is Sold?
Deferral sounds like a loophole until you look at the interest. Norway prices the wait at its policy rate plus five points, and Britain already runs a ten-year instalment option in inheritance tax.
What About Founders Whose Shares Cannot Be Sold?
A founder cannot sell a fifth of a company to settle a tax bill. Norway defers for up to three years and charges interest; Spain exempts the holding altogether, and pays for that elsewhere.

