The speed with which the financial markets have been getting back to business is astonishing, given the human suffering and disruption in New York. But we are now heading into a very testing time for the industry.

Since the attacks on the US, central banks around the world have moved with alacrity to head off the risk of a systemic crisis, pumping huge amounts of liquidity into the banking system. The authorities have also been bending over backwards to ensure banks help out corporate customers, even if it means bending the rules.