Britain's Financial Services Authority (FSA) said on Wednesday the three men, aged 33, 37 and 39, who are not linked to any other current insider dealing investigation, were in custody awaiting questioning after six premises were searched.
The men have not been charged and are expected to be released on bail later on Wednesday. The FSA declined to comment further.
The three are London professionals working in the fund management industry and are all employed at firms in the capital, one source with knowledge of the investigation said.
The arrests come one month after the FSA and police swooped on two men and three women, including a trader at asset manager Schroders , for suspected insider dealing. They were later released on bail.
Britain's top financial regulator, which has vowed to crack down on a crime that once went largely unpunished, is prosecuting six others for insider dealing. It has secured 21 convictions for the offence, which can carry a jail sentence of up to seven years.
The FSA's highest-profile insider dealing investigation to date stems from raids in March 2010 that saw seven men arrested, including employees of Deutsche Bankand Moore Capital, in an operation codenamed Tabernula.
Another three individuals were later held as part of the same operation, although only seven have been charged so far.
The FSA said one of them, Paul Milsom, a former equities sales trader at the investment arm of Legal & General , had indicated at a pre-trial hearing he would plead guilty to one count of insider dealing.
(Reporting by Kirstin Ridley; Editing by Greg Mahlich)