Writedowns by Fannie Mae, the US mortgage financier that was nationalised this year and AIG, the insurer that has twice been bailed out by the US government, have lifted total losses reported by financial institutions since the beginning of 2007 to $918bn, according to data compiled by Bloomberg.

While the mounting writedowns are evidence that financial institutions are grappling with the scale of their problems, they also suggest that losses have deepened as a result of the market turmoil that followed the collapse of Lehman Brothers, the Wall Street bank, in September. Last month the International Monetary Fund raised its estimate of the likely total losses in the financial sector to $1,400bn, from $945bn in April.

Banking analysts are predicting further pain in fourth-quarter results, which are expected to have suffered from further falls in the price of many of the residential and commercial mortgage backed securities they hold on their balance sheets.