It has suddenly become respectable to ask the question: what would happen if the euro broke up? Last week’s rise in German bond yields signalled that the scenario was being taken more seriously by investors. I am told that London law firms are allocating large amounts of time to examining the validity, following a break-up, of cross-border contracts written in euros. And, to judge from my own inbox, asset managers are starting to ask about the economics of how it could occur.

When the euro was created, the process took many years of careful planning. The European Currency Unit, a basket of fixed amounts of national currencies, traded for several years before its name was changed to the euro on January 1 1999.

This movie cannot be run backwards. It is hard to imagine the 17 members of the eurozone going through a decade-long process in which national currencies would first be reintroduced, then gradually allowed to deviate against each other within narrow bands, then ultimately allowed to float freely. Much more probable is a severe crisis, followed by the reintroduction of some national currencies, after which the “euro” might be retained by some current members, or cease to exist altogether.