Lloyds Banking Group lost hundreds of thousands of dollars in cash after a senior foreign exchange dealer allegedly tipped off a counterpart at BP about a $500m currency deal.
According to Bloomberg, four unnamed sources said Lloyds found out that a dealer, Martin Chantree, alerted a trader at BP of the bumper FX swaps deal, which the bank was planning to execute regardless of market price movements at a certain time.
However, during the seven minutes before Lloyds began executing the trade at 10:53 GMT on 31 January 2013, the pound tumbled by 16 basis points against the dollar, costing the bank $750,000 (£451,000, €541,000).
Bloomberg's sources say that Chantree told fellow traders that maybe he shouldn't have shared the information.
Chantree has since been suspended, say sources.
Lloyds had not returned calls for comment, on the report or Chantree's employment status, at the time of publication.
In November last year, Lloyds launched an "internal review" of FX trading at the group, after a raft of regulatory investigations into the potential manipulation of the currency markets hit the industry.
"We are aware that a number of regulatory and enforcement authorities are investigating foreign exchange trading and, as a result, we believe it is prudent to review our own foreign exchange trading over recent years and have commenced such a review," said Lloyds.
The daily $5tn currency market is the largest in the financial system and is pegged to the value of funds, derivatives and financial products.
Morningstar estimates that $3.6tn in funds, including pension and savings accounts, track global indexes.
Lloyds has relatively small role in the FX markets, compared to leading banks Deutsche Bank and Citi, as industry statistics show it ranks 39th in the spot and currency-forwards business.
BP has 200 traders which execute deals in energy, commodities and FX contracts. Although the group does not isolate trading unit profits in its financial results statement, in 2004 it revealed that it made $2bn in this business area alone.