Unlike people, capital has no nation. It can just move effortlessly from France to Switzerland to the Cayman Islands. That's why single-country initiatives to e.g. tax wealth (or even tax extremely profitable companies) are doomed to failure: those assets are easy to transfer and hide; if the UK passes a progressive wealth tax, all those global billionaires will just sell their empty houses in London and buy empty houses somewhere else.

Hence the proposal by many economists that the only solution is a broad agreement on a global progressive wealth tax, with at least the major blocs of the US and EU on board. See e.g. "A Brief History of Inequality".