Eight people in London and the south-east were arrested yesterday as a part of a major insider trading investigation, the regulator the Financial Services Authority (FSA) has revealed.
An operation involving 40 FSA staff along with officers from City of London Police was launched as a part of the watchdog's ongoing investigation into insider dealing rings.
The FSA has not used its powers against insider trading since 2001, but currently there are three cases involving five defendants before the courts.
Workers from Swiss investment bank UBS and JPMorgan Cazenove are reported to have been arrested in the latest swoop.
UBS confirmed to the Financial Times that a junior member of staff had been suspended while the FSA investigation takes place.
A subcontractor at JPMorgan Cazenove is also believed to one of those arrested.
The case is thought to involve the banks' printing presses where information on upcoming deals is alleged to have been used before being made public.
Last week the FSA started its prosecution of Malcolm Calvert, a partner at investment bank Cazenove, on 12 charges of using insider information.
Mr Calvert entered a plea of not guilty.
Earlier this month the FSA also fined IT professional John Shevlin £85,000 for using information gained from confidential emails at his employers the Body Shop to make a £38,472 profit on betting the retailers share price would fall by using a contract for difference (CFD).