A former RUC Special Branch officer was being questioned last night by detectives investigating the leaking of transcripts of telephone conversations between the British Prime Minister's chief-of-staff and Mr Martin McGuinness of Sinn Féin.
Police files, a computer and disks were also seized when officers raided a house in Northern Ireland. Security sources confirmed that the former policeman worked as a low-ranking officer with the intelligence agencies.
The transcripts published in the Times and the Irish News detailed conversations between Mr McGuinness and Mr Jonathan Powell as well as the former Northern Ireland secretary, Dr Mo Mowlam.
At the time Mr McGuinness was Northern education minister.
Sinn Féin accused MI5 of tapping the phones and compiling the transcripts which feature in a new paperback biography of Mr McGuinness, Martin McGuinness: From Guns to Government by Liam Clarke and Kathryn Johnston.
In one dated July 16th, 1999, Mr Powell allegedly called the former Ulster Unionist MP for West Tyrone, Mr William Thompson, "an ass".
According to the Irish News, Mr McGuinness told Mr Powell that day: "I think the unionist strategy is very, very clear . . . They are not interested in the Ireland Ministerial Council. All you have to do is listen to William Thompson last night on BBC2". The transcript suggests Mr Blair's chief-of-staff replied: "Ah, he's an ass".
Two days later, in a conversation with Mr McGuinness, Dr Mowlam spoke of her resistance to being moved back to England.
She allegedly said: "I've been called across to see the Prime Minister tomorrow. I'm fighting like f--- to stay, but I don't know what will happen. . ."
Mr Adams and Mr McGuinness, in a transcript of a phone conversation on September 22nd, 2001, are also reported to discuss fears that the UUP was trying to collapse the Executive.
Mr McGuinness said yesterday: "There are people within the British intelligence services who in the course of some 25 years have not been able to accept the implications of the peace process and the change that that peace process brings."
- (PA)