The dramatic collapse of Lehman Brothers, AIG’s appeal for aid and the forced sale of Merrill Lynch sent shockwaves across financial markets on Monday. The S&P 500 closed at its lowest level in nearly three years and recorded its biggest one-day fall for seven years as investors fled from risky assets.

“There is a sense today that the financial landscape has changed irrevocably,” said Peter Dixon, UK economist at Commerzbank.