A cloud no larger than a betting slip - but one that could be joined by some rather larger, darker, formations - has moved over European monetary union.

Last March, Intrade, the (appropriately) Irish-based online betting site, started a contract called "Euro dropped 2010". It would pay off at 100 if, by December 31 2010, "any current user [were] to drop euro currency", as Intrade puts it.