Hong Kong-based financial consultant Yoshimitsu Sasago is unsettled by developments since the recent leak of client data from a Panama-based law firm.

Sasago has served Japan-based clients in Hong Kong for the past 10 years. Sometimes they ask him to provide a perfectly legal but somewhat tricky service: to help set up a very small — apparently shell — company in an offshore tax haven such as the Cayman Islands or British Virgin Islands, and then to open an account for that company at a major bank in Hong Kong.

"No information is disclosed, so no one can tell which company is owned by whom at all. That's the juiciest part of a tax haven firm," Sasago told The Japan Times by phone.