The FSA has fined Barclays almost £2.5m for failing to provide accurate reports to the regulator.
Data provided by Barclays Bank and Barclays Capital Securities contained a number of discrepancies and errors, which the FSA says hampered its investigations into market abuse.
The firms were fined a total of £2.45m for their poor reporting, and have been ordered to improve systems and controls.
Firms are required to provide the FSA with data of reportable transactions by close of business the day following a trade execution, which the regulator uses to investigate insider trading and market abuse.
While reviewing a suspected incident of market abuse by a third party, the FSA discovered a number of discrepancies in Barclays's data.
The discovery led to a full review of Barclays's systems and controls, which were found to be inadequate, causing errors in the data submitted to the FSA.
Alexander Justham, director of markets at the regulator, says: "Complete and accurate transaction reports are an essential component of the FSA's market monitoring work.
Barclays' reporting failures could have a damaging impact on our ability to detect and investigate suspected market abuse."
Barclays received a particularly high penalty for its actions due to the seriousness of the breaches and as a warning to others, the FSA says.
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