And the regulators invented the Basel system of risk-weighted capital ratios, which stipulates different leverage ratios for different categories of loan, in theory to take account of the riskiness of those loans.

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And Nationwide's balance sheet, on paper at least, is stronger than that of any of the big banks, with loss-absorbing core capital equivalent to 12.5% of risk-weighted assets, 2.5 percentage points higher than the banks' capital ratios.

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