"How exactly that is configured is a detailed matter for negotiation. But that principle must be upheld, and a mansion tax actually is a very economically sensible way of doing it.
"But there are different ways of doing it. It can be done through local government as well as central government. And providing the principle is accepted - that taxation should be related to property - and there are vast numbers of extraordinarily valuable properties now around in the south of England, netting very large gains for their owners, many of whom come from abroad incidentally.
But will they avoid the unintended (but perhaps desirable) consequence of all "wealth" being devalued to a value just below where it becomes taxable?