HSBC's head of global foreign exchange cash trading has been arrested and charged in the US for allegedly conspiring to commit wire fraud on a £2.7 billion transaction.
The US Department of Justice said Mark Johnson, 50, allegedly conspired to defraud an HSBC client through a "front running" scheme that netted over £6 million.
The Briton, who lives in the US, was detained on Tuesday as he landed at JFK International Airport and released on Wednesday on 1 million dollar (£755,000) bail.
Johnson was charged along with a second Briton, Stuart Scott, 43, HSBC's former head of foreign exchange cash trading for Europe, the Middle East and Africa, who lives in the UK.
The pair are accused of misusing information in 2011 "provided to them by a client that hired HSBC to execute a foreign exchange transaction related to a planned sale of one of the client's foreign subsidiaries".
According to prosecutors the pair, along with other traders they directed, bought sterling for HSBC's "proprietary" accounts prior to converting about 3.5 billion dollars (£2.7 billion) in sales proceeds on behalf of the client into sterling, knowing the large transaction would boost the price of the pound.
The "front running" enabled them to generate 8 million dollars (£6 million), some of it illegally, to the benefit of HSBC and at the expense of their client, it is alleged.
Robert Capers, US attorney for the Eastern District of New York, said: "As alleged, the defendants placed personal and company profits ahead of their duties of trust and confidentiality owed to their client, and in doing so, defrauded their client of millions of dollars."
The client was not identified, although the sale was said to relate to part of its ownership interest in an Indian subsidiary.
Assistant attorney general Leslie Caldwell said: "The defendants allegedly betrayed their client's confidence, and corruptly manipulated the foreign exchange market to benefit themselves and their bank."
She added: "This case demonstrates the criminal division's commitment to hold corporate executives, including at the world's largest and most sophisticated institutions, responsible for their crimes."
A lawyer for Mr Johnson declined to comment. HSBC is not accused of any wrongdoing and declined to comment.