I need to know more details but my inclination is that they would have argued that the account represented a foreign investment, so it was not bound by UK tax law, and/or it was a business, not personal account (businesses can be called anything really, so Rosie 47 could be included), so subject to corporation tax, not income tax, which has much bigger tax reliefs (most of the amount put in there would likely not be chargeable at all if this was the case). However, my knowledge is limited and I don't know details of offshore accounts, and I also think there would be an issue with the evidential burden.