Director Adam Feeley said it will look at a number of related-party transactions after an extensive preliminary inquiry, and will coordinate its work with the Securities Commission and Registrar of Companies.

"We have concluded a number of cases which now enable us to address issues identified in the preliminary inquiry," Feeley said. "The investigation will focus on a small number of related party transactions which will ensure we complete the investigation in a timely manner."

Last week the SFO added new investigations into South Canterbury Finance, the WSD group of companies that were formerly chaired by ex-Progressive MP Matt Robson to its growing list of cases, and Crafar farm bidder Natural Dairy NZ.

In July, the Securities Commission accused the financiers' directors of misleading investors in some of its offer documents, and is pursuing civil and criminal charges. The board was made up of Rick Bettle, Terence Butler, Ann Butler, Paul Forsyth, Robert Barry and Vance Arkinstall, who had to step down from his role as chief executive of the funds management lobby group, Investment Savings and Insurance Association.

Dominion Finance was sent to the receivers in 2008, owing $176.9 million to some 5,900 investors, after it failed to negotiate a moratorium. North South was spared after its trustee agreed to an orderly supervised wind down, but later asked to be placed in receivership after the charges were made.