I have friends who are now a very wealthy couple in their 50's
They have worked VERY VERY hard all their lives. They both got excellent degrees - not without a significant amount of personal effort, and then have worked hard on their careers to build up to the point they are at now.
Obviously they have paid tax and national insurance on their income through-out their working lives, for much of it they will have been in the high taxation bands, and currently continue to pay income tax at the top level. When their children were small, they both still worked hard, and employed people like a nanny and a gardener. These employees were paid out of the income of my friends which had already been taxed. Tax and NI was then paid on that money earned by the Nanny and the gardener. So in effect, Tax was paid twice on some of my friends income.
They live in a VERY large, very beautiful house which must have cost a great deal . They will have paid a significant sum in stamp duty when it was bought (as they did on their previous property). Stamp-duty itself is already a form of 'mansion tax'.
They have money to spend, and when they spend it, they pay 20% in VAT on most of it (just about everything except basic foods of course).
So yes, they are 'rich', but every month they are already contributing more to the taxation system.
What is 'fair' or equitable about suddenly demanding more money from them just because they have more than most others?
If we didn't have people able and prepared to work to acquire that sort of wealth, to pay standard taxes every month, then the tax revenue would fall significantly. And if we over-tax those who are capable of making a lot of money, many of them will go and live somewhere else.
This plan is nothing more than 'envy politics', and I would have no truck with it.