The O'Higgins Commission of Inquiry has found that former minister for justice Alan Shatter took allegations of garda whistleblowers very seriously.

The unpublished report said he had very substantial concerns and had displayed active and personal concern.

Given that most of the allegations had been examined or were previously reviewed, the actions of the then minister were amply justified, it believes.

In relation to former garda commissioner Martin Callinan, the report states that clearly and unambiguously there was not a scintilla of evidence to support any allegation of any type of corruption.

The commission found that any aspersions on his integrity were unfounded and deeply hurtful.

It also said that exchanges between the garda commissioner, the justice minister and the Department of Justice were at all times professional and appropriate.

The commission also found that garda whistleblower Maurice McCabe acted out of genuine and legitimate concerns.

It concluded the garda sergeant showed courage and performed a public service at considerable personal cost.

The commission believes he is due the gratitude of the general public and also An Garda Síochána.

While some of his complaints were not upheld by the commission, it found that he was a man of integrity, who the public can trust in his duty as a garda.

The final report said Mr McCabe impressed the commission as being never less than truthful even if prone to exaggeration at times.

Mr Shatter resigned as minister in 2014 after a report by a senior barrister concluded that he had failed to heed the voice Sgt McCabe.

It led to the establishment of the commission, which commenced in February 2015 and was initially scheduled to complete its work within one year.

The Minister for Justice later agreed to a request from Mr Justice Kevin O'Higgins to grant an extension to the commission to 29 April.

The commission's report was submitted to the Minister Frances Fitzgerald yesterday and she is consulting with the Attorney General to arrange for it to be published as soon as possible.