Ten days ago Henry Paulson, the US Treasury secretary, responded to alarm over the prospects of Fannie Mae and Freddie Mac, the twin “government-sponsored” – but privately owned – giants of US housing finance. Mr Paulson asked for authority to lend them whatever it would take to keep them afloat, or to shore up their capital by buying their equity, or both.

This power is to be appended to a bigger housing market measure that Congress has been considering, with its usual urgency, for months, and whose arrival on the president’s desk is promised imminently. What US taxpayers may wish to know is how much the fiction that Fannie and Freddie would never be a charge on the public purse is, in the event, going to cost them.