Tens of thousands of British citizens born in the US but who left when only a few months or years old risk having their bank accounts in Britain frozen because of intense pressure by US tax authorities on UK banks.

In one case, a 74-year-old living in Cambridge has been sent increasingly urgent letters from Barclays demanding her American tax identification number, even though she left the US on the RMS Queen Elizabeth in 1947 when she was just 18 months old. She had assumed that her US citizenship had lapsed.