Further, it is assumed that bonds are relatively safer than stocks in the short run, but stocks outperform relative to bonds in the long-run.

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As well, holders of the banks' senior bonds, which many investors have assumed would be safe from losses, may also lose money.

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The original rescue plan assumed that, starting in 2012, Greece would issue new bonds to pay off maturing ones.

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Many schemes assume, on the basis of past performance, a return of 7.5-8%, a figure that is highly implausible given the current low yields. (By contrast, in 1981, when Treasury bonds were yielding 13.5%, pension funds assumed a future annual return of just 6%.) Such rosy assumptions allow schemes to stint on their contributions, building up huge future risks.

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The company assumed it would have to offer a rate 0.3-0.5 percentage point higher than government bonds when it went to the market last month, said Masatoshi Hoshi, its head of treasury and accounting.

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