RBS has confirmed it faces not only a monetary fine but also other unspecified sanctions in relation to the LIBOR fixing scandal.
The bank, which is 82% owned by the UK government, said it is in talks with the FSA, the Commodity Futures Trading Commission and the United States Department of Justice, to agree a sum following investigations into the bank's "submissions, communications and procedures around the setting of the LIBOR".
The figure is estimated to be around £500m, and although RBS has yet to confirm this, it warned shareholders today that the fine would be substantial.
It also revealed there could be other punishments dished out as a result of the scandal.
It said in a statement: "Although the settlements remain to be agreed, RBS expects they will include the payment of significant penalties as well as certain other sanctions."
Speculation has been mounting over the amount RBS will be fined in recent days and Chancellor George Osborne has urged the organisation to cut bankers' pay rather than let taxpayers pick up the bill.
Other banks have already been punished. Barclays was fined £290m in June 2012 by UK and US regulators while Swiss bank UBS has also been forced to stump up an astonishing £930m in penalty fees paid to the UK, US and Swiss regulators.
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