The Supreme Court has begun hearing an appeal by senior counsel Sean Guerin against a Court of Appeal decision that he reached highly critical conclusions about former minister for justice Alan Shatter, in breach of Mr Shatter's constitutional rights.

The Appeal Court made a declaration that conclusions in Mr Guerin's 2014 report, examining how garda whistleblower Sergeant Maurice McCabe's complaints were dealt with, were reached in breach of fair procedures and constitutional and natural justice.

The declaration came after Mr Shatter won his appeal against the High Court's rejection of his challenge to the report.

Mr Shatter claimed Mr Guerin should have interviewed him before reaching adverse conclusions or allowed him to respond to draft conclusions.

He said the report had caused him to resign from office after it was published and his good name and reputation had been destroyed.

The Court of Appeal said Mr Guerin was obliged to observe the rules of natural justice and of letting the other side be heard.

Today, lawyers for Mr Guerin began making submissions on his appeal to the Supreme Court.

Senior Counsel Paul Gallagher said it was his view that the matter was more complex than the Court of Appeal seemed to have considered it to be.

He submitted that Mr Guerin was asked to carry out a scoping exercise urgently and to express an opinion on whether there was a sufficient basis for concern about the way Sergeant McCabe's complaints were investigated. 

He said Mr Guerin was given eight weeks to do this and it was not open to him to embark on a process which would greatly exceed the time allowed. 

Mr Gallagher said Mr Shatter knew at all times that he was potentially within Mr Guerin's terms of reference. 

He said Mr Guerin was required to express an opinion and his report would have been of little use if he had not but he said Mr Guerin's opinions were not conclusive findings.

The court was told it was open to the Government not to have published the report immediately or to have allowed Mr Shatter to make submissions before it was published. 

Mr Gallagher said these were decisions which were made politically.

Mr Gallagher argued that if such a scoping exercise could be challenged in the courts, then the inner workings of the Government were susceptible to judicial review.  He said it would be difficult to get anyone to express an opinion or produce any report urgently. 

He said reports to Government by civil servants would also be open to challenge in the courts, and he suggested that Government could not operate in that way.

Lawyers for the former minister for justice told the court that Mr Shatter's claim had been repeatedly mischaracterised by Mr Guerin.

Senior Counsel Paul Sreenan said Mr Shatter was not asserting that he had a right to remain as minister for justice or to have his role as minister excluded from the inquiry.

He said Mr Shatter's claim was a simple one: his good name had been attacked in Mr Guerin's report, without him being afforded fair procedures.

Mr Sreenan said Mr Guerin had interviewed Sgt McCabe on four separate occasions over 19 hours.

He asked why Mr Guerin could not have sought a meeting with Mr Shatter or put the potential criticisms to him in writing. He said it would not have taken long.

Mr Sreenan submitted that Mr Guerin had not appealed the findings of the Court of Appeal that his criticisms of Mr Shatter were gravely damaging to Mr Shatter's good name.

He also said there had been no explanation on affidavit as to why Mr Guerin did not offer Mr Shatter the "right to be heard" when in a different part of his report, Mr Guerin described that right as fundamental.

Lawyers for Mr Shatter will continue making their submissions in the afternoon. The court is expected to reserve its judgment.