But there are now concerns that the Fed itself may be exhausting its $800bn (£399bn) stock of assets. It has swapped almost $300bn of 10-year Treasuries for questionable mortgage debt, and provided Term Auction Credit of $130bn.

"The steep rise in swap spreads this week is ominous," said John Hussman, head of the Hussman Funds. "The deterioration is in stark contrast to what investors have come to hope since March."

Lehman Brothers took writedowns of just $200m on its $6.5bn portfolio of sub-prime debt in the first quarter even though a quarter of the securities had "junk" ratings, typically worth a fraction of face value.

Willem Sels, a credit analyst at Dresdner Kleinwort, said the banks are beginning to face waves of defaults on credit cards, car loans, and now corporate loans. "We believe we're entering Phase II. The liquidity crisis has eased a little, but the real credit losses are accelerating. The worst is yet to come," he said.

The jump in corporate bankruptcies has not yet been picked up by the usual indicators, which tend to lag the market, lulling investors into a false sense of security. The true losses are already known to specialists in the business, said Mr Sels.