The aggregate effect contributed about as much to post-tax return on equity last year as was lost to writedowns, and dwarfed the boost to returns from cost control and bonus cuts.

They focus obsessively on the latest year's pre-tax profits, or perhaps post-tax earnings.

But work by two academics, Thomas Piketty and Emmanuel Saez, shows that inequality has been just as marked in pre-tax as in post-tax incomes.