Belfast developer Gareth Graham has had detailed discussions with two US law enforcement agencies regarding the €1.6 billion sale of Nama's Northern Irish loan book to New York investment fund, Cerberus.

The so-called Project Eagle sale in April 2014 is the subject of criminal and parliamentary investigations following claims that £7 million transferred from Belfast lawyers Tughans to an Isle of Man account was destined for a number of Northern Irish political figures.

Mr Graham, who is taking legal action against Cerberus, spent the last two days outlining concerns related to the fund’s purchase of the loans to the US Department of Justice and the Federal Bureau of Investigation (FBI).

It is understood the talks were detailed, and that ahead of meeting him agency staff had read the official account of evidence Mr Graham gave this month to the Northern Assembly's Finance and Personnel Committee, which is inquiring into the deal.

In the course of that evidence, Mr Graham told the committee that recorded telephone conversations showed a former member of Nama's Northern Ireland advisory board, Frank Cushnahan, had set out to destroy the value of his property investment firms.

Before relations between them broke down, Mr Cushnahan was chairman of the Graham family bookmaker’s chain and a director of the property group, made up of four companies. Mr Graham said Mr Cushnahan still held a 5 per cent stake in it.

Nama bought their £33 million debt from Bank of Ireland and sold it to Cerberus as part of Project Eagle. Mr Graham maintains that Cerberus benefitted from Mr Cushnahan's efforts to destroy the value in his property business.

Cerberus has always maintained that it acted properly throughout. It told the committee in writing last week that, to the best of its knowledge, no improper payments were made on behalf of it or any of its affiliates in connection with Project Eagle.

Mr Cushnahan did not appear before the committee but his lawyers wrote to say he disputed the developer’s evidence and that there was no conflict of interest in his role on the Nama board, as he was no longer a shareholder in the Graham property business. He also denies having any contact with Cerberus.

One of the original Project Eagle bidders, another New York-based fund, Pimco, withdrew from the auction in March 2014 after it told Nama that it had agreed to pay £5 million each in success fees to Mr Cushnahan, Tughans and US lawyers, Brown Rudnick.

Cerberus later hired Brown Rudnick, which brought in Tughans as local counsel.