Banks were aware of unusual currency trading at a key period during the trading day four years before regulators began an investigation into the manipulation of the so-called 'London fix', according to reports.
The Daily Telegraph reports that the BBC said it has seen research by Morgan Stanley showing the banks were concerned about the London fix - a key rate that is widely used by pension funds and other investors to value portfolios and set a price for deals - as far back as 2009.
The Morgan Stanley analysis was said to have uncovered unusually sharp movements in exchange rates at around 4pm - the point at which the London fix is set each day through counting currency trades over a one-minute period.
It warned that anyone trading at that time was unlikely to get the best possible deal on the day, and that it could have 'debilitating' effect on investments costing up to 5% annually.
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