A retired garda detective known as 'The Badger', who had a close working relationship with British intelligence, is to be called as a witness in the trial of a former Sinn Féin ard comhairle member and IRA gun-runner.

Lawyers for Gerry McGeough, who is accused of trying to kill a UDR man almost 30 years ago, are keen to cross-examine the Badger. McGeough, from Co Tyrone, is the first republican to be tried for historical crimes since the Good Friday Agreement.

The prosecution claims he was injured when he tried to kill UDR man Sammy Brush in 1981. It is alleged that Brush returned fire and that McGeough was treated for a gunshot wound in St Vincent's hospital in Dublin and later Monaghan County Hospital.

The Badger was one of several gardaí sent to guard the wounded man, alleged to be McGeough, in Monaghan County Hospital and to arrest him when he was discharged. However, the patient escaped before he could be arrested.

In 2007, the Badger made a statement about this incident to gardaí. This statement is part of the prosecution case. Although the prosecution haven't listed the Badger as a witness, McGeough's lawyers want to cross-examine him.

Solicitor Peter Corrigan said: "We have requested that he be called as a witness. Around six other guards are already due to give evidence via video link from the Four Courts."

McGeough's lawyers are consulting with former MI6 officer turned whistle-blower Fred Holroyd, who met the Badger several times. Holroyd said the detective gave information on republicans to British intelligence.

Although gardaí kept their relationship with British intelligence secret because of the political sensitivities at the time, the Badger met MI6 with the full knowledge and authority of his superiors, Holroyd said.

In his statement, the Badger describes how the patient in Monaghan County Hospital, alleged to be Gerry McGeough, had feebly walked the corridors in a dressing gown, pyjamas and slippers, complaining of pain.

That evening, a young man who said he was McGeough's brother arrived with three women to visit the patient. Four IRA men – including Jim Lynagh who was killed by the SAS at Loughall six years later – also visited. Gardaí then saw the women, and what appeared to be the first young man, leave after 30 minutes. The young man walked out normally. Gardaí later discovered it was actually the patient dressed as his visitor.

McGeough's trial, which was postponed after he became ill and underwent emergency heart surgery six weeks ago, is due to resume next week.