Peter Adamson, 50, a retired detective, was found not guilty last Friday after a court in Ballymena, Co Antrim, was told the crown would offer no evidence against him because the prosecution was not considered in the public interest.

The documents allegedly leaked to Liam Clarke, Northern Ireland editor of The Sunday Times, and Kathryn Johnston, his wife, were transcripts of tapped phone conversations recorded by MI5 and Special Branch at the home of Martin McGuinness, Sinn Fein’s chief negotiator from 1998 to 2001.

The transcripts are of conversations between McGuinness; Gerry Adams, the Sinn Fein president; Jonathan Powell, chief of staff to the prime minister; and the late Mo Mowlam, then Northern Ireland secretary.

In them, Mowlam addresses McGuinness as “babe” and outlines her differences with Tony Blair while Powell describes unionist MPs as “asses”. Mowlam authorised the tap.

The content of the calls, including the “babe” reference, had been referred to in The Sunday Times in 2002 and the documents were reproduced in full as an appendix to a biography of McGuinness by Clarke and Johnston entitled From Guns to Government, published in April 2003. On the night of the book’s publication, Adamson’s home was raided by armed police who arrested him. The next evening there was a similar raid on the home of Clarke and Johnston and on the office of The Sunday Times in Belfast, where police battered down the door. Clarke and Johnston were taken to a terrorist holding unit and questioned over a 20-hour period.

It later emerged that the warrants used in the raid on the journalists’ home and the Sunday Times office were unlawful.

Nuala O’Loan, the Northern Ireland police ombudsman, subsequently ordered disciplinary action against eight officers from constable to chief superintendent. In a highly critical report, which was accepted without dispute by the police service of Northern Ireland, she condemned the police action as “a poorly led and unprofessional operation” and listed 32 separate breaches of the rules committed by the officers.

“It is a big relief to myself and my family who possibly suffered even more than I have,” Adamson said through his solicitor.

Jeffrey Donaldson, the DUP MP for Lagan Valley, has championed the case. “This was a man who served the community well and saved countless lives as a result of his police expertise,” he said. “Yet he had to endure all of this while former terrorists are able to walk the streets.”

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