Shares in Lehman Brothers fell over 30% on opening this morning amid fears that clients could pull business and Moody's trimmed its outlook for the bank's debt, citing fears over liquidity and asset concentrations in a move that sparked fears that it could be the second US investment bank to collapse under the weight of the credit crunch.

Moody's senior vice president, Blaine Frantz said: "Rising illiquidity across financial markets has resulted in asset concentrations on Lehman's balance sheet that have proven to be somewhat larger than optimal for the firm."