Developer Gerald Conlan will be forced to supply documents and information on how Anglo arranged the deal to prop up its stock market value.
The move came after a landmark ruling allowed under the Criminal Justice Act, which was only placed on the statute last month.
It was sought by the Director of Corporate Enforcement, Paul Appleby, who applied in Naas District Court to force Mr Conlan to explain how the 2008 deal took place. Mr Conlan, who had refused to co-operate, has now agreed to make himself available.
Mr Conlan was part of the so-called “Anglo 10” secret investment group, which also included K Club co-owner Gerry Gannon and developer Joe O’Reilly.
“The orders granted . . . require Mr Gerald Conlan to produce certain documents and information related to Anglo Irish Bank’s provision of a substantial loan to him for the purchase of its shares in July 2008,” a spokesperson for Mr Appleby said after the court move.
It is the first time the Criminal Justice Act has been used to force a witness to assist investigations, and will be seen as a significant development in uncovering a key issue in the financial crisis, as it relates to how and why Anglo lent the group, described as long-standing clients, €451m in July 2008 to buy 10% of the bank.
The deal was lined up to prevent the stake acquired by businessman Sean Quinn from becoming available on the stock market.
Such a move could have altered control of the financial institution.
Investigations are also examining a so-called bed and breakfast deposit transfer arrangement where €7 billion was moved out of Irish Life & Permanent and into Anglo in September 2008.
David Drumm, Anglo’s former chief executive, is in the middle of a bankruptcy case in the US and has so far resisted efforts by Irish investigators to question him.
Anglo’s wind-down will cost the public €25bn to €30bn.