The Greek and Swiss government will soon sign a deal under which Greek authorities will be able to retroactively tax previously undeclared assets of Greek citizens stashed away in Swiss banks . . . it is unclear how much money Greek nationals have saved in Swiss accounts but Helvetia, a Swiss financial intermediary, estimates it may reach 20 billion euros, virtually all of which has not been taxed . . . the Greek central bank estimates that around 70 billion euros have been concealed in foreign bank accounts . . . the Greek government will be eager to present the treaty to its international lenders and voters at home as an evidence of its anti-tax evasion drive as between 40 and 45 billion euros, about 12% of the country’s GDP, remain untaxed . . . however, it is not clear how effective the tax deal will prove since previous agreements with other European countries, on which this one was modelled, had been undermined by a series of loopholes . . . Greece has been plagued by its citizens moving their savings out of Greek banks due to concerns that the country could leave the euro and devalue it currency, a move that could possibly cause the value of Greek bank accounts to drop by half or more.