Investigators are analysing computer equipment for evidence of insider trading, following the first joint operation between the Financial Services Authority (FSA) and the Serious Organised Crime Agency (Soca)
Investigators searched a total of 16 addressees in the early hours of 23 March, seizing computers and documents.
Six men were arrested on suspicion of being involved with insider trading, after an operation that began in late 2007 involving 143 FSA workers and Soca staff.
"It is believed that the city professionals passed inside information to traders - either directly or via middlemen - who traded based on this information and have made significant profits as a result," said the FSA.
Peter Sommer, visiting professor at the London School of Economics, who is an expert witness in cases involving complex computing evidence, said the FSA will use its own internal experts and private sector specialists to analyse devices.
The FSA's Surveillance and Automated Business Reporting Engine (Sabre) was upgraded in 2008 to provide real-time alerts to potential financial abuses.
"The monitoring systems will highlight suspicious activity, but by looking at the personal computers, laptops, cell phones and blackberries etc the FSA can put its finger on it," said Sommer.
He said the raids would have to be carried out quickly because the people involved are "bright enough to get rid of the information on devices."