Barclays has set aside £500 million over the alleged rigging of foreign exchange (forex) markets which are being probed by regulators around the world.
It adds to penalties and compensation costs it has already had to shoulder to deal with other scandals such as payment protection insurance (PPI) mis-selling and a £290 million fine for Libor rate-rigging in 2012.
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In the UK, the Serious Fraud Office (SFO) and the Financial Conduct Authority (FCA) have both launched investigations into the alleged manipulation of the £3 trillion-a-day forex market.
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FCA chief executive Martin Wheatley has described the claims as "every bit as bad" as the Libor scandal that has cost banks billions in penalties.
Barclays announced the provision as it published results showing a 4% rise in pre-tax profits to £1.22 billion for the third quarter.
It said a £500 million provision had been recognised "relating to ongoing investigations into foreign exchange with certain regulatory authorities".
The bank also added an additional £170 million to its pot of money for settling PPI compensation claims.
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