In the frantic political seizure triggered by Athens’ abortive referendum plan, European leaders broke what was once the eurozone’s big taboo: that Greece could default and leave the eurozone.

The possibility has long been discussed in private, not least in Germany. But for the eurozone’s leadership – especially France – the avoidance of default and preservation of the euro’s integrity was a core goal of the seemingly endless rescue plans and negotiations to keep Greece from crumbling under the weight of its public debt.

Only last week, Nicolas Sarkozy, the French president, said in a national broadcast that a Greek exit would be a “catastrophe” for Europe and the world. The mood has now shifted dramatically, with Mr Sarkozy and Angela Merkel, the German chancellor, discussing the prospect in public as they heaped pressure on George Papandreou, the Greek prime minister, to back away from his call for a plebiscite on the €130bn bail-out for Athens.