At Prime Minister's Questions, Mr Cameron said the manipulation of the key Libor inter-bank borrowing rate by Barclays traders was "outrageous" and those responsible for "spivvy and probably illegal activity" should be held to account.

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As I pointed out last week, timing is critical to detect schemes using financial statement manipulation, and benchmarks are key.

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Oil producers would seem to be the ones most likely to sell oil and drive prices down, but some of them also have access to physical supplies, key to any real manipulation.

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