JPMorgan sues former London Whale boss

A sign is seen outside the JPMorgan office in Los Angeles, California, October 12, 2010.

LONDON (Reuters) - JPMorgan Chase & Co has filed a suit in a British court against the former boss of Bruno Iksil, the trader known as the London Whale, for the outsized derivatives positions he took that cost the bank $6.2 billion in losses this year.

Javier Martin-Artajo, who was Iksil's immediate supervisor, was named a defendant in a London lawsuit filed on October 22.

Details of the court filings, which were first reported by Bloomberg News, will not be released until the defendant acknowledges the claim, the court said.

JPMorgan executives said in July the bank would act to take back pay from traders and supervisors involved in the loss. Those included Iksil, Martin-Artajo, and Achilles Macris, who was Martin-Artajo's boss.

A JPMorgan spokeswoman in New York declined to comment. Martin-Artajo's lawyer could not immediately be reached for comment.

(Additional reporting by David Henry in San Francisco; Editing by Gerald E. McCormick and Sinead Cruise)