Within the euro area, official discussion of the topic was completely taboo until French President Nicolas Sarkozy and German Chancellor Angela Merkel raised the possibility of a Greek euro zone exit last month. The survival of the currency came first, they said.

"That immediately released the shackles on governments to contingency plan for that reality," says Alastair Newton, a former UK Cabinet Office and Foreign Office official and now chief political analyst for Japanese bank Nomura. "Before that, they couldn't plan because if they did it would leak out and then it could become a self-fulfilling prophecy."
...
British newspapers have been full of stories about Foreign Office planners drawing up emergency schemes to assist or even evacuate Britons from a collapsing euro zone. Government officials declined comment on specific stories but some said they were re-examining long-held assumptions about Europe's stability.

...in Europe, the mere admission that Plan B is a possibility, apparently set off a chain of events that makes Plan B an inevitability: "...officials there feared that releasing the information could fuel further doubts and instability in the euro zone."
...
The U.K. Foreign Office has begun making contingency plans to evacuate U.K. residents from Spain and Portugal in the case of bank meltdowns in those countries, said a person familiar with the matter. In a sign of concern over stirring panic, a spokesman was tight-lipped about details apart to say that office is always preparing for all types of scenarios.

Logistics and law enforcement also need serious thought, experts say. Capital and border controls might need to be tightened as states leaving the euro try to replace one currency with another. "While the public might tolerate capital controls, ATMs shutting will not be tolerated," said the British official, speaking on condition of anonymity. ...

Originally posted by Dbriefed

Why evacuate U.K. residents from other countries?

Back the the Reuters article on the 7th:

Logistics and law enforcement also need serious thought, experts say. Capital and border controls might need to be tightened as states leaving the euro try to replace one currency with another. "While the public might tolerate capital controls, ATMs shutting will not be tolerated," said the British official, speaking on condition of anonymity. ...

Tough to survive in a foreign country during social unrest, your cash falls in value, and banks can't give you more cash.