Former Justice Minister Alan Shatter was forced to take High Court action after Taoiseach Enda Kenny snubbed his objections to the damning report on garda whistleblower allegations which led to his resignation.
Since he was forced from office, Mr Shatter made several attempts to raise concerns with the Taoiseach about barrister Sean Guerin's review of garda whistleblower Sgt Maurice McCabe's allegations of malpractice in the force.
However, sources close to the sacked minister claim he came up against a "wall of silence" and the legal action he initiated against Mr Guerin last week was a final resort.
Mr Shatter's court case will cause huge embarrassment for the Taoiseach, as he appointed Mr Guerin to conduct the investigation and pledged to implement his recommendations. Mr Shatter wrote to the Taoiseach's office three times after his resignation and twice used the Dail chamber to air his criticisms of Mr Guerin's report.
"Alan tried to quietly set out his problems behind the scenes but he didn't get any response from the Taoiseach - even after he set out his stall in the Dail," a source said.
"He resigned for the good of the Coalition and he knows this is not going to change.
"He did not want to go to court but he is concerned about the reputational damage he suffered and the implications for future inquiries."
The Taoiseach's own involvement in the garda whistleblower controversy will be thrust again into the spotlight as it emerges an internal investigation by his office exonerated Mr Kenny's handling of Sgt McCabe's penalty point allegations when he first raised them two years ago.
The investigation was initiated following a complaint from Sgt McCabe in which he claimed the Taoiseach's office "fobbed" him off when he gave them "documentary evidence of criminality".
In an email sent to Mr Kenny's office in November 2012, Sgt McCabe said: "I reported to An Taoiseach's office serious corruption, perverting the course of justice and misappropriation of public money.
"It is almost four months since I reported the malpractice to An Taoiseach's office and no one has ever contacted me concerning my allegations."
The internal review completed by the Taoiseach's department in January 2013 found no breach of its customer service charter.
However, it acknowledged there were "wider concerns" which were under investigation by An Garda Siochana.
The investigation by Assistant Commissioner John O'Mahony did not support Sgt McCabe's penalty point claims.
But an independent review by the Garda Inspectorate eventually vindicated him, while Mr Shatter's handling of the controversy contributed to his own downfall.
Last week, Mr Shatter issued legal proceedings aimed at quashing findings made against him in Mr Guerin's review of Sgt McCabe's allegations of garda malpractice in Cavan. Mr Shatter resigned the day before the report was published and a review of the Department of Justice set up after Mr Guerin's inquiry led to secretary general Brian Purcell stepping aside.
Mr Shatter's central concern with Mr Guerin's report is that he was not interviewed or given a right to reply to the findings.
However, garda whistleblower John Wilson said he had "little sympathy" for Mr Shatter, as he previously accused Sgt McCabe and him of failing to cooperate with the garda penalty point inquiry.
"We never got an opportunity to give our evidence to the garda investigation and Mr Shatter accused us of failing to cooperate," he said.
"I can't say I have much sympathy for him now he's jumping up and down because he did not get to have his say."
Mr Shatter later apologised for saying they did not cooperate.
Last week, the Sunday Independent revealed Mr Shatter wrote to the Taoiseach after his resignation claiming he was "stymied" by Department of Justice officials.
He claimed officials failed to give him advice he sought from the Attorney General's (AG) office on Sgt McCabe's allegations and he only learned of the response on reading the Guerin Report.
Mr Shatter claimed the AG advised against holding a statutory inquiry into Sgt McCabe's allegations, which contradicts Mr Guerin's recommendations and the Taoiseach's promise to establish a Commission of Investigation. This will form part of Mr Shatter's legal challenge.
In an affidavit lodged with the courts this week, Mr Shatter claimed Mr Guerin acted "unreasonably" and "unfairly" by not interviewing him as part of his inquiry.
He also claims Mr Guerin carried out his investigation with "indecent haste" and did not review crucial evidence from the Garda Ombudsman.