Tim Geithner, the US Treasury secretary, acted to shield Citigroup’s bondholders and management from accountability at the height of the financial crisis while taxpayers were left on the hook, a former US bank regulator has alleged.

Sheila Bair, who served as chairman of the Federal Deposit Insurance Corp during the crisis and its aftermath, levelled fresh attacks at Mr Geithner, the Obama administration, fellow financial regulators and bankers such as Vikram Pandit, Citi’s chief executive, in a new book that has laid bare policy disagreements of the past few years.