Europe's leaders meet again on Thursday. The question they must answer this time is not whether they can rescue this or that country, but whether they can rescue the eurozone - if not the European Union in its current form.

To see why, we just need to review the last 12 months. In July 2011, Europe's leaders agreed on a limited restructuring of Greek debt, while at the same time making financial assistance nimbler and cheaper. A year later, Greece remains on knife-edge.

Throughout last autumn, they agonized over the rise of Spanish and Italian bond rates, until finally the European Central Bank decided to administer pain relief in the form of large-scale liquidity provision to banks. But, despite the arrival of new, reform-minded governments in both Italy and Spain, the relief proved short-lived.