Critics of U.S. spending on the United Nations got a huge boost—and supporters of that spending, especially the Obama Administration, took a body blow—from an unlikely source this week: the British government, long one of the U.N.’s staunchest supporters. In a sweeping and hard-nosed reorganization of priorities for its $10.6 billion multilateral foreign aid program, the Conservative-Liberal Democrat coalition government of Prime Minister David Cameron has pulled the financial plug entirely on four U.N. agencies at the end of next year, put three others judged merely “adequate” on notice that they could face the same fate unless they improve their...