The world has not ended. The international economy has not yet collapsed. But one thing is now quite clear: the banking system as we know it has failed.

Following the disappearance of Bear Stearns in March, and now the bankruptcy of Lehman Brothers and the surprise plans for Bank of America to absorb Merrill Lynch, three of Wall Street's five big independent investment banks have disappeared inside six months. After an astonishing weekend it is too early to predict the future shape of investment banking with confidence, but business as usual is not one of the possibilities.