Former minister for justice Alan Shatter has won an appeal over his failed challenge to parts of a report which concerned his handling of complaints by Garda whistleblower Maurice McCabe.

The three-judge Court of Appeal unanimously granted Mr Shatter’s appeal over the High Court’s rejection of his challenge to barrister Seán Guerin’s May 2014 report.

The appeal was heard last June before the president of the Court of Appeal, Mr Justice Sean Ryan, Ms Justice Mary Finlay Geoghegan and Ms Justice Mary Irvine. Mr Shatter was not in court for the decision.

In his judgment, Mr Justice Ryan said Mr Shatter had established he was a person whose constitutional rights were in jeopardy by reasons of the conclusions that Mr Guerin was proposing to include in his report, that Mr Guerin was obliged to observe the rules of natural justice and there was a breach of those rights because of the defective procedure that was adopted.

Mr Shatter was entitled to a declaration in those terms. For those reasons, he would allow the appeal, he said.

He also adjourned to a later date the precise terms of any other reliefs to which Mr Shatter might be entitled.

The judge added that he entirely agreed with the High Court as to the severe pressure under which Mr Guerin was working in dealing with a large volume of documentary material under severe time constraint.

In the overall context of what Mr Guerin had to do, “I am very far from being personally critical of him”, he said.

In her concurring judgment, Ms Justice Finlay Geoghegan also allowed the appeal and found the Guerin report was amenable to judicial review. Ms Justice Irvine agreed.

In his appeal, Mr Shatter argued the Guerin report made “findings of fact” and reached conclusions which were “highly critical” of him without affording him fair procedures or the right to be heard before it was given to the Taoiseach, who later published it. He said he had “no alternative” but to resign after the report.

While the findings of the O’Higgins Commission that Mr Shatter acted properly at all times might go some way to alleviate the damage, the Guerin report directly caused Mr Shatter’s resignation and damage to his good name, it was argued.

Mr Guerin denied any unfairness and argued his report contained “observations”, not conclusions, based on documents provided for the review by the Department of Justice.

Mr Guerin was asked by the government, of which Mr Shatter was then a part, to prepare a “scoping” report and the consequences that flowed were a result of “purely political decisions”, it was argued.

Lawyers for Mr Guerin also argued he gave Mr Shatter the fair procedures required of a “scoping exercise” such as this was and there was “ample basis” for the High Court’s finding against Mr Shatter on all grounds and describing several of his claims as “extraordinary and unstateable”.

They also disputed arguments by Mr Shatter that the Guerin report was inconsistent with the O’Higgins Commission report.

The O’Higgins report confirmed the absence of any document recording any decision of the minister on the McCabe complaints and an issue in the department about documents not getting to the person they were intended for, it was argued.

Other complaints by Mr Shatter were internal issues for the department.