When Lehman went bust, other Banks struggled to measure their exposure because Lehman turned out to be not a single institution but a tangle of many entities.

A team led by the chief risk officer, and helped by Booz Allen, a consultancy, is sifting through thousands of internal documents to gauge the impact of their release.

"Punitive actions are a good way of deterring people," said HSBC's Mr Mahendran.