THE LAST FOUR YEARS have created what economists call a “natural experiment” in economic policy. As a consequence of deregulation and globalization, Britain and the United States experienced the financial crisis of 2008 in much the same way. Large parts of the banking system collapsed and had to be rescued; the real economy went into a nosedive and had to be stimulated. But after 2010, the United States continued to stimulate its economy, while Britain chose the stonier path of austerity. The British are no more wedded to the idea of fiscal austerity than are the Americans.