From the end of 2019, expatriate US persons must provide their US tax identification number (TIN) to their local banks, or risk having their bank accounts closed or frozen.

Under the Foreign Account Tax Compliance Act (FATCA), which came into effect in July 2014, all foreign financial institutions (FFIs) must identify their US clients and report them to the US Internal Revenue Service (IRS). FATCA is intended to prevent US taxpayers from evading US income tax on offshore investments and assets, in part by penalising foreign institutions that do not report identifying information about their US shareholders, clients or investors to the IRS.

Originally, the intention was to enforce this by applying a 30 per cent withholding tax on payments to any FFI that did not comply, but in practice all major countries enacted legislation forcing their financial institutions to comply with FATCA.

The original FATCA regulations required FFIs to collect their US clients’ TINs and dates of birth, and report them to the IRS, but...