NAMA has revealed that it asked a firm to withdraw from the Northern Ireland loan book sales process after expressing "serious concerns" over proposed payments to a former adviser.
Frank Cushnahan, a Nama Northern Ireland adviser until November 2013, and ex-partner at Tughans Ian Coulter were said to have been involved in trying to set up the sale to investment company Pimco.
The 850-property portfolio was eventually sold to New York investment firm Cerberus in April last year for more than £1bn.
It is understood at least one informal meeting with Pimco was held at Stormont that involved the pair and a senior politician.
The US firm had told The Irish News that an "unsolicited approach" was made, but it did not progress a deal and raised its concerns with Nama.
Nama has revealed it asked Pimco to withdraw from the sales process in March last year after discovering the proposed fee arrangements between Tughans and Mr Cushnahan.
A spokesman said Nama had "serious concerns", particularly the proposed payment to one of its former advisers.
It added that Mr Cushnahan "never had access to confidential information but the Nama board determined this arrangement could undermine the integrity of the sale".
Mr Cushnahan, who was on the Nama Northern Ireland advisory committee from 2010 until 2013, worked from an office in Tughans' Marlborough House building in Belfast.
The firm said: "In Frank Cushnahan's capacity as a local businessman, he was a referrer of work to the practice and other NI law firms.
"He had a self-contained office in the same building occupied by Tughans, as did other entities over the years."
Tughans indirectly acted for the buyers of Nama's portfolio in the north.
The firm is being investigated by the Law Society of Northern Ireland after professional fees were found in an offshore account controlled by Mr Coulter.
It is thought the Law Society has been unable to establish what work Tughans carried out to earn millions of pounds in fees.
Mr Cushnahan was one of two external members nominated to the Nama Northern Ireland advisory committee by the then finance minister, the DUP's Sammy Wilson.
The businessman has had roles including chairman of the Belfast Harbour Commissioners and maintenance firm Red Sky.
In 2011 he became the first ever Catholic to address the Presbyterian General Assembly.
Mr Cushnahan's lawyers told the BBC he is satisfied that he complied with his fiduciary and statutory obligations as a member of Nama's Northern Ireland advisory committee.
Cerberus said they were represented by the US firm Brown Rudnick, who in turn instructed Tughans in Belfast.
The New York-based capital management firm said "no improper or illegal fees were paid by us or on our behalf".
Nama has said it is "fully satisfied" that the sales process for the north's loan portfolio "delivered the best possible return".
