What would happen if one of the 25 member states of the European Union refused to ratify the constitutional treaty? This question usually elicits one of two responses. Some say the non-ratifying country would have to leave the EU. Others argue that nothing would happen: the EU would simply continue on the basis of the existing treaties. It is a choice between a nasty divorce and permanent political stalemate.

Faced with such a choice, one might want to consider a third alternative. An intriguing possibility would be to split the EU in two - an outer part, in which all members take part, and the eurozone. This is not the same as "variable geometry" - the idea that countries should choose à la carte the parts of European integration they want to adopt and the parts they want to avoid. The former would be a more inflexible arrangement. The outer part would consist of a customs union, a common external trade policy, an internal market, a single competition policy and free movement of goods, services, labour and capital. This is essentially today's EU minus the eurozone and perhaps also minus the common agricultural policy, structural funds, and the common foreign and security policy.