The British government put pressure on police to release IRA terror suspects after a request to Downing Street from Gerry Adams, a former police chief has claimed.
Retired PSNI Detective Chief Superintendent Norman Baxter told a Westminster inquiry on the on-the-runs letters controversy there was "a culture within the Northern Ireland Office to ensure republicans were not persecuted".
He claimed pressure was put on police by the NIO to pave the way for some suspects, a number of who were "high-profile members of Sinn Fein", to return to the UK.
Mr Baxter told the Northern Ireland Select Affairs Committee of political pressure placed on police, citing the example of the arrests of two men in connection with the attempted murder of a part-time UDA soldier.
A phone call from the British government in 2007 was made at the request of Sinn Fein President Mr Adams, within hours of the arrests.
Gerry McGeough and Vincent McAnespie had been detained in relation to the attempted murder of Ulster Defence Regiment soldier Sammy Brush near Aughnacloy in 1981.
"They were arrested, I have a note here, on the 8th of March some time around tea time and taken to the serious crime suite at Antrim," said Mr Baxter.
"At 9.10pm I received a phone call from the duty ACC (Assistant Chief Constable) at (PSNI) headquarters.
"Gerry Adams had telephoned Downing Street demanding their release, Downing Street rang the Chief Constable's office looking their release and I got a phone call suggesting I should release them.
"That, of course, in my mind is attempting to pervert the course of justice and that was conveyed back to headquarters."
He added: "I don't know who the personality in Downing Street was but as a police officer that is totally illegal and unconstitutional.
"We continued interviewing them and Mr McGeough was subsequently convicted for attempted murder."
Mr McAnespie was acquitted at trial of charges related to the 1981 gun attack.
Under the on-the-runs letters process, names of individuals who feared they were wanted fugitives were passed to the government, the majority through Sinn Fein, asking for an assessment of their status.
Mr Baxter said officers involved in Operation Rapid – set up by the PSNI in 2007 to review those regarded as 'wanted' for terrorist offences before the Good Friday Agreement – had no idea letters sent out by the force were being used as part of a political administrative scheme.
Mr Baxter told the Westminster committee that he believed the Northern Ireland Office had acted far beyond its legal remit by sending letters to OTRs, and he added that any political interference undermined police investigations.
Former Assistant Chief Consable Peter Sheridan also gave evidence to MPs yesterday.
Both men were mentioned a number of times the legal judgment by Mr Justice Sweeney at the Old Bailey in February which led to the dropping of charges against alleged Hyde Park bomber John Downey and the subsequent scathing criticism of the PSNI.
Mr Baxter yesterday said he and the PSNI has been scapegoated over the collapse of the Downey case. He described criticism of the PSNI by Theresa Villiers as "disgraceful" and accused Chief Constable Matt Baggott of "poor leadership" over his handling of the situation.