The FSA has fined spread betting firm City Index £490,000 for transaction reporting failures.
The regulator says the spread betting firm failed to submit accurate reports in respect of 2 million transactions.
It says the failings occurred between November 2007 and September 2009 and the failings represented nearly 60 per cent of its reportable transactions.
It failed to report approximately 55,000 transactions and reported approximately 1,970,000 transactions with one or more data fields completed improperly.
The FSA says these breaches occurred despite the regulator sending repeated reminders to firms of their obligations to provide accurate data.
Managing director of enforcement and financial crime Margaret Cole says: “City Index failed to report accurately a high proportion of its transactions for almost two years. This failure is a serious breach of our rules because it can have a damaging impact on our ability to detect and investigate suspected market abuse.
“Firms and their management must ensure they submit quality transaction reporting data and we encourage all firms to review the integrity of this data on a regular basis. We will continue to monitor the quality of firm reporting and we are committed to taking action where necessary to ensure firms comply with their reporting obligations.”