While politicians and central bankers continue to debate the merits of European sovereign bonds, so-called E-bonds, many appear not to have noticed that one has – to all intents and purposes – already been launched.

Fans of E-bonds believe they could signal a closer step towards fiscal unity in the European Union, reduce the cost of borrowing for Europe's weakest states and - potentially - save the euro. Opponents say they would increase the cost of borrowing for stronger economies.