In an insider-trading investigation that could become the U.K.’s biggest case related to the crime, three employees from major banks have been arrested, reported Bloomberg and other media quoting two people with knowledge of the situation.

The sources reportedly have said that the National Crime Agency, which is assisting with covert surveillance and the U.K. Financial Conduct Authority is working with the National Crime Agency. The sources were not named in the media reports as they didn’t want to be identified because the investigation is private. The sources further said that he identities of the arrested people were not disclosed by the authorities and that the arrests of the works were carried out in recent months and more are planned.

In a report by the government on the so-called Panama Papers scandal, an insider-trading probe was made public last week. A task force had “identified a number of leads relevant to a major insider-trading operation” led by the FCA and supported by the NCA, the briefing said. The task force has been set up to investigate leaked documents from a Panama law firm.

A spokesman for the crime agency declined to immediately comment and officials at the regulator declined to comment.

The FCA concluded a major trial in an insider-trading case dubbed Operation Tabernula about six months ago and this latest news is one that follows the previous case. With a record 4 1/2 year sentence handed to ex-Deutsche Bank AG corporate broker Martyn Dodgson, these two men were convicted by a jury earlier this year. Another suspect is yet to be tried and three other individuals pleaded guilty in the case.

As was in the case that was played out in Tabernula issue, in this latest case also the partnership between the FCA and NCA in the investigation is similar. In what was the first time the U.K. watchdog had ever used such techniques, covert surveillance on some of its targets was carried out in 2008 by the regulator who had recruited the NCA’s predecessor, the Serious Organised Crime Agency to do so at that time.

A very important aspect and a point of reliance in the trial was a conversation between two of the defendants from a bug placed in one of their offices.

Opting to file civil complaints, the regulator had never prosecuted anyone for insider trading prior to 2008 and the FCA has cracked-down on insider trading since 2008. Since that time, including a number of individuals from high-profile institutions such as Moore Capital Management LLC and Schroders Plc., the regulator has racked-up 31 convictions related to the crime.

With Mark Lyttleton, a former BlackRock Inc. portfolio manager, pleading guilty to improperly trading shares and call options ahead of public announcements, the regulator had another big win last week. He will be sentenced in December.

(Adapted from Bloomberg)