The U.K Financial Services Authority’s determination to get tough on insider dealing continues. Last week it sought to extradite a suspect for the first time, now it has raided addresses and made arrests in what it says is its biggest ever operation against insider dealing.

In its first joint operation with officers from the Serious Organized Crime Agency, a branch of the Police, the FSA made dawn raids on 16 addresses in London and across the country. Some 143 FSA staff were involved.

The FSA seized documents and computers from residential and business premises and made six arrests. Two of those arrested were described as “senior city professionals at leading city institutions,” another was a “city professional at a hedge fund.” A seventh person was arrested the next day.

The regulator said they were suspected of being involved in a sophisticated and long-running insider dealing ring that generated “significant profits.”

The FSA did not reveal the names of the people arrested or the companies they worked for. But they include Julian Rifat, a hedge-fund trader at the London arm of Moore Capital Management. Moore said it was “co-operating fully with the FSA in its investigation.” Rifat’s lawyers said he was “deeply distressed by the accusation and is working to clear his name as soon as possible.”