The last thing the world's banks needed right now was a rogue trading scandal.

In the past six months, they have been buffeted by large trading losses triggered by the subprime mortgage crisis in the US and market turmoil has raised fundamental questions about their business model. They are facing severe capital constraints and the prospect of an abrupt economic slowdown. Even before Société Générale's shock announcement, most bankers were already deeply apprehensive about the future.