The plans, which call for a "haircut" of at least 30 per cent on deposits above €8,000, sketch out an increasingly likely scenario for at least one bank, the sources said.

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A Greek bail-in could resemble the rescue plan agreed by Cyprus in 2013, when customers' funds were seized to shore up the banks, with a haircut imposed on uninsured deposits over €100,000.

It would be implemented as part of a recapitalisation of Greek banks that would be agreed with the country's creditors — the European Commission, International Monetary Fund and European Central Bank.

"It [the haircut] would take place in the context of an overall restructuring of the bank sector once Greece is back in a bailout programme," said one person following the issue. "This is not something that is going to happen immediately."

Eurozone officials said no decision had been taken to wind up any Greek banks or initiate a bail-in of depositors, a process that would be started by the ECB declaring the banks insolvent or pulling emergency loans. Andrea Enria, chair of the European Banking Authority, said on Saturday he was not aware of any plans to introduce haircuts to retail depositors of Greek banks.