LONDON—As the euro-zone debt crisis intensified in recent months, at least two global banks took steps to install back-up technology systems that could handle trades in old European currencies like drachmas, escudos and lire.
That, the banks quickly found, is not so easy in a financial world that is trying to both exhibit confidence in the ailing euro and—just in case—plan for its possible demise.
Technology managers at the banks contacted Swift, the Belgium-based consortium that manages the network used in financial transactions, said people familiar with the matter. The banks wanted Swift's technology support and the currency codes that would be necessary to set up the backup systems.
But Swift declined to provide some information for such contingency planning, including whether old codes could be used in the system, said the people familiar with the matter.
That is partly because officials there feared that releasing the information could fuel further doubts and instability in the euro zone, these people said.
It is a relatively minor setback for banks, as they look at everything from loan agreements to the safety of their branch staff in the event of one country's withdrawal from the euro currency.
But it illustrates the road blocks that politicians, banks and companies in Europe face as they attempt to simultaneously prepare for a euro-zone break up while assuaging market fears.
"As soon as you start contingency planning . . . it can become a foregone conclusion," said Alastair Newton, senior political analyst at Nomura PLC. "But if things go wrong and you don't have plans in place, you're in trouble."
Such planning comes as the idea of euro-zone break-up is still frowned upon in many corners.
European Central Bank President Mario Draghi this past week said that such speculation about the euro's demise is "morbid."
Nevertheless, governments, finance firms and corporations have been quietly stepping up plans in the past several weeks to prepare for a worst-case scenario.
The Financial Services Authority, the U.K.'s bank watchdog, has sent letters to the country's major banks asking for updates on their level of preparedness, and a similar dialogue has begun between banks and regulators in the U.S. in recent weeks, said the people familiar with the matter.
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.
In another sign of escalating fears, some corporate firms with operations in Greece and elsewhere in Southern Europe have begun transferring their cash out of Greece on almost a daily basis—compared to the normal two-week interval—as a precaution against a sudden loss in value if currencies are revived, said a banker familiar with the companies' transactions.
Prepping their systems to handle codes for old European of currencies is one way banks are taking steps to buffer themselves against major business disruptions if any country suddenly leaves the euro zone.
Currencies have three letter codes—such as USD for U.S. dollars—that banks use in a wide range of financial transactions, from complex investment-banking trades to the basic transfer of money. The codes are set by the Geneva-based International Standards Organization, and used by Swift, which is a co-operative company that formats and sends payment orders for some 10,000 firms in more than 200 countries.
One question banks have, and have not been able to clarify, is whether codes for now-defunct currencies, such as GRD for the Greek drachma, will be valid in the current Swift system.
A Swift spokesman said the company is ready to take whatever actions are required to maintain normal operations, but that "it is not appropriate this time for Swift to comment on issues specifically associated with the euro zone."
If a new currency emerges, it is handled by a maintenance agency affiliated with the International Standards Organization. A spokesman for that agency, SIX Interbank Clearing Ltd., said the agency has several projects looking at "dire scenarios" but the contingency plans for such scenarios have so far remained confidential.
Once a bank knows what the code is, it is relatively simple to set up a program for that new currency, according to technology experts. The bank must then tweak its infrastructure for expected volume and ensure data for counter-party banks are correct. Systems must then be modified and tested, said a technology executive at a bank in London, a process which takes one to two weeks.
Write to Sara Schaefer Munoz at Sara.Schaefer-Munoz@wsj.com