Once again, even more spectacularly than before, the world is confronted by the bizarre phenomenon of one bank trader, apparently without anyone else's knowledge or co-operation, running up a multi-billion loss.

The term "rogue trader" has entered common parlance since Nick Leeson brought down Barings Bank in 1995 by hiding a £860m trading position in Singapore. Jérôme Kerviel seems to fit the classic pattern of a rogue trader, from his astonishing losses to the fact that it is hard to fathom why he acted as he did.