Representatives of a Belfast businessman battling to stop his companies being put into administration are working in shifts 20 hours a day to listen to thousands of hours of taped phone calls, the High Court has heard.

Counsel for Gareth Graham also revealed that concerns around the process already raised with the National Crime Agency, the PSNI and US law enforcement bodies are also set to be referred to authorities in the Irish Republic.

Mr Graham is a director and major shareholder in STH 500 and Lehill Properties, which own a variety of commercial and residential premises in Belfast. The firms' loans were among those transferred over to Nama.

Last year, US investment fund Cerberus snapped up Nama's entire Northern Ireland portfolio, Project Eagle, in a deal worth more than £1 billion.

Mr Graham is now locked in a court fight to try to win back control of his companies. He is challenging Cerberus’ right to put them into administration, claiming his businesses were financially strong and never missed a repayment.

Earlier this month he appeared before a Stormont inquiry into the sale of Nama’s Northern Ireland loan book. Mr Graham told the committee he has recorded business phone calls, which allegedly show an “ingrained culture of inappropriate and possibly illegal conduct” across political, banking, legal and accountancy sectors.

In court Tuesday, his lawyers asked a judge for another two weeks to complete an examination of the tapes before they have to lodge points of claim to support his argument about impropriety in the process.

Monye Anyadike-Danes QC insisted work is continuing to get the legal documents ready.

“We were instructed that the directors have recently identified evidence of possible illegality and that may undermine the validity of the appointment Cerberus held,” she said.

“My clients have thousands of hours of telephone conversations to listen to, some of which may bear on the matter... quite a lot probably don’t because every phone call ever made by their practices was recorded.”

She said some calls that the company directors had already identified would seem to be relevant.

No attribution of any suspected illegality was made in court.

Seeking another fortnight to finalise the analysis, Ms Anyadike-Danes added: “They have people listening 20 hours a day in shifts.”

The barrister also confirmed her client’s concerns have been alerted to authorities on both sides of the Atlantic.

She said: “It’s been referred to the National Crime Agency, it’s been referred to a US law enforcement organisation, it’s been referred to the PSNI, and I believe it’s about to be referred to the relevant authorities in the Republic of Ireland. There’s been no shortage of taking the relevant steps.”

Opposing the move, David Dunlop, for Cerberus entity Promontoria Eagle, urged the judge to press on with the case as it currently stands.

“The explanation given for wishing to extend time is because of looking at various tape recordings held by Mr Graham and which may or may not give rise to further allegations,” he said. “Whether or not there are issues that come to light, these are matters that can be developed in due course.”

But with a trial hearing in the case not due to take place until January, Mr Justice Horner agreed to give Mr Graham’s lawyers the two weeks to file their claims.

“There won’t be any extensions that imperil the hearing date,” he warned.