Do you think the money is on those small islands? Or on Guernsey? Or the British Channel Islands? No, the money is in New York and London at the usual banks who earn money on fees and can work with the deposits. The banks on those islands don't have a data center, or a bank vault. They only legally have the money on paper, but "their" money is in the banks in NYC (Caribbean) and London (former Empire).

Interesting read "Treasure Islands: Tax Havens and the Men who Stole the World", Nicholas Shaxson