GEORGE TOWN, Cayman Islands — What happens to a tax haven when it has to raise taxes? The Cayman Islands may soon find out. Caught in a vise of shrinking revenue and stubbornly high public spending, the Caymans averted a fiscal crisis this week by securing a $60 million overseas loan. But the Foreign and Commonwealth office in Britain, which oversees the Caymans and can veto foreign lending requests, has delivered an ultimatum: The rest of the $284 million the Cayman government says it needs will not be forthcoming until this offshore financial center imposes spending cuts and considers some...