The US Treasury should have disclosed a change in accounting methodology which allowed it to announce a huge reduction in the cost of the Troubled Asset Relief Program (Tarp), according to a report released this week by the office of the Tarp special inspector-general (Sigtarp), Neil Barofsky.

The Treasury recently cut its estimated loss from the 2008 part-nationalisation of AIG from $45 billion to $5 billion. But, the report said, "there is a serious question over how much of this decrease