When news broke that Jérôme Kerviel, a young trader at French bank Société Générale, had lost the firm €4.9bn on unauthorised trades, the spotlight fell on what had been one of the bank’s least glamorous trading desks and, until then, considered a low-risk operation. The desk is known as Delta One.

Such units look after routine business and take their name from the flow of equity derivatives that closely track their underlying asset. If that moves by 10%, the derivative will move by very close to 10%, meaning it has a delta of one.