“Brown Rudnick is fully supportive of efforts to clarify the issues that have been raised over this matter and will give every assistance to the relevant authorities,” said a spokesman.

It comes after a Stormont finance committee yesterday met to draw up a list of firms and people it will invite to its inquiry into the matters of the Project Eagle sale.

It plans to invite all parties — including law firms and the rival hedge funds Cerberus and Pimco — which were involved at any stage in the sales process, as well as Nama board members. The controversy flared last week after Independent TD Mick Wallace revealed the existence of a £7m (€9.8m) Isle of Man bank account.

He claimed the money was earmarked for a Northern Ireland politician.

A DUP member of the Stormont committee, Paul Girvan, said the inquiry needs to move quickly to establish the truth .

“There is merit in trying to get this cleared up,” said Mr Girvan. “Because there is a lot of rumour and while there is that, there is enough of a cloud hanging over this place with a view to everything that goes on, and now to have implications that there is a politician potentially involved in what is a dirty scheme.”

Tughans — a leading firm of Belfast solicitors, which was effectively involved as a sub-contractor to Brown Rudnick working for the winning bidder Cerberus — said the Isle of Man account was under the control of a former senior staff member.

Tughans said it had retrieved the money and reported the matter to the Law Society of Northern Ireland.

Cerberus said it had assured Nama, following confirmations from Brown Rudnick and Tughans, that no payment was made or due to be made to any current or former adviser of Nama.

The Stormont committee said it would use its powers to compel witnesses to attend, if necessary. The Dáil’s Public Accounts Committee meets on Thursday to consider how it will probe the Project Eagle controversy.

It was unclear last night whether Nama board members would attend the Stormont hearings, which could begin next week.

The Project Eagle transaction involved loans worth €5.7bn. The loans had been advanced by Dublin banks to northern borrowers during the boom years.

The loans were secured on about 850 properties, including large swathes of Lagan-side commercial office blocs that had transformed Belfast in recent years. After the Nama auction, the loans were sold to Cerebus for €1.6bn. Brown Rudnick initially advised giant US fund Pimco,

but Pimco pulled out in early March 2014 after the Nama board raised “serious concerns” about a payments arrangement the law firm proposed to make to a former member of Nama’s Northern Ireland advisory committee.

In April 2014, Cerberus, which was by then also being advised by Brown Rudnick after the departure of Pimco from the sales process, won the bid. Cerberus is known in Dublin and Belfast as the purchaser of a chunk of discounted loans from Ulster Bank in the North.

Nama yesterday reiterated its confidence in the sale process which was overseen by international investment house Lazards.