Three City firms were hit with fines totalling £4.2 million today after repeatedly failing to provide trading figures which help the regulator spot market abuse.
The Financial Services Authority (FSA) fined investment bank Credit Suisse £1.75 million, market maker Getco Europe £1.4 million and broker Instinet Europe £1.05 million.
More than 1,000 City firms provide around eight million transaction reports to the FSA every day to help it investigate potential insider trading and market manipulation.
But the FSA said the trio had committed "multiple breaches" in not providing prompt and correct data despite several reminders to the wider market in 2007 and 2008.
Director of markets Alexander Justham said: "Without quality data we cannot properly detect and investigate market abuse, identify market wide risks or have a comprehensive understanding of the activities of each firm.
"This data is vital in our efforts to combat financial crime and we will continue to pursue firms that fail to provide quality data."