City of London

A square mile with its own laws, its own police — and, per lore, everyone's money.

The Square Mile is not London: it has its own Lord Mayor, its own police, a permanent official — the Remembrancer — seated in Parliament to watch legislation, and a franchise where businesses vote. It survived William the Conqueror by negotiation and every government since by the same method. When the theories need a capital for the money power, they don't have to invent one; the medieval corporation is right there, wearing robes.