After the global banking system hit the buffers and regulators began the laborious task of remodelling the rules on bank capital, they soon reached two conclusions: there had to be more of it and, in the next crisis, it had to save the taxpayer money.

After watching the fallout from the failure of Lehman Brothers, they were reluctant to let holders of Tier 1 debt bear losses once a bank had eaten through its equity capital. In the 2008 crash the result was that taxpayers were the ones to pick up the bill when a bank hit serious trouble while holders of the bank's junior bonds - typically professional investors - seemed to escape the pain.