RTÉ News has learned that former garda commissioner Martin Callinan wrote to the Department of Justice more than two weeks ago about the recording and retention of telephone conversations in garda stations.
In a letter to the Secretary General of the department, Mr Callinan asked that Minister for Justice Alan Shatter be informed of details of the recordings.
In the letter he also says that he consulted with the Attorney General on 11 November 2013.
He says he had established a working group to deal with the issue and report to him once they had consulted with the AG's Office.
The letter, entitled "Recordings of Telephone Conversations made and retained in Garda Stations", which has been seen by RTÉ News, says the recordings, which are now in court proceedings, took place in the 1990s.
They are of members of the Garda Síochána and members of the public.
The former commissioner said the systems were set up in the 1980s to enable gardaí to record calls to and from control rooms; in particular 999 calls, bomb threats and other messages.
The practice continued in some stations over the years with recordings retained in the garda stations.
The original recording systems were replaced by dictaphones during the 1990s and by another system in 2008.
In the letter, Mr Callinan also says that he directed that routine recording of non 999 calls to garda stations cease and confirmed in the letter to the department that all recordings except 999 calls ceased nationally on 23 November 2013.
The total number of tapes is over 2,400 and Mr Callinan says in the letter that he consulted with the AG and expected to consult with the Data Protection Commissioner.
He said the AG advised that all outstanding recordings be brought together and an inventory be made identifying the station, the date and the condition of the tapes.
The former commissioner said the recordings are now being stored and an inventory has been compiled and sent to the AG's office. He said some tapes were mouldy and may be unplayable.
He stressed, however, that as soon as the issue came to his attention he took immediate steps to regularise the position and continues to do so.
Govt says Shatter only learned of issue yesterday
A Government spokesman said tonight that Mr Shatter only found out for the first time yesterday about the recording and retention of telephone conversations in garda stations, despite the fact that a letter informing him about them was sent to the Department of Justice more than two weeks ago.
The spokesman also said that Taoiseach Enda Kenny only found out about the issue on Sunday, when he was contacted by the AG.
Mr Callinan said in the letter he had informed the AG about the recordings four months ago.
The spokesman acknowledged the existence of the letter from the former commissioner to the Secretary General of the Department of Justice.
The spokesman said he does not know when the Attorney General, who sits at Cabinet, knew about the issue.
He said "the Government as a collective" did not know and the Minister for Justice found out for the first time just after 6pm yesterday.
Minister for Finance Michael Noonan said tonight he could not answer why Mr Shatter was not aware of a GSOC report in June, which recommended that the commissioner might re-evaluate the practice of recording phone calls.
He said he presumed the department was aware but did not think it was an important issue at the time.
Speaking on RTÉ's Prime Time, Mr Noonan said it is the contents of a particular tape in a particular piece of legislation that "has raised this to the importance that the Taoiseach had to get involved immediately and set a Commission of Investigation in place".
He said: "We're not happy, the Taoiseach isn't happy, that's why there is a Commission of Investigation".
Mr Noonan said he had full confidence in the Minister for Justice.
The minister reiterated his confidence in Mr Shatter saying he is a very good minister and there is no suggestion that he did anything improper, "so he shouldn't resign".
Inquiry into taped phone calls at garda stations
Earlier today, the Government announced that it is to set up a statutory Commission of Investigation after learning that "a system was in place in a large number of garda stations whereby incoming and outgoing telephone calls were taped and recorded".
In a statement, the Government said: "From the information available, the practice of making recordings was in place for many years and was discontinued in November of 2013.
"It is not yet clear why this practice was in operation."
Mr Callinan was told of the Government's plans to launch the independent investigation into the recording of phone calls last night.
A senior minister has confirmed to RTÉ that Mr Callinan was also told of the unease felt in Cabinet about the practice.
After being informed of the issue by the Attorney General on Sunday, the Taoiseach briefed the Cabinet this morning.
A review and verification of the practice carried out yesterday showed it was widespread.
The spokesman said there was no contact between Mr Kenny and the commissioner and that the Taoiseach only found out about Mr Callinan’s decision to step down this morning.
Mr Noonan earlier told RTÉ's Six One News that the issue of the taping of phone calls came to the attention of the Attorney General arising from litigation that was being pursued.
He said that when AG Máire Whelan established the preliminary facts, she briefed the Taoiseach sometime over the past 48 hours.
He said Mr Kenny thought the issue was of sufficient magnitude and concern to take personal command of the events and he came to Cabinet this morning with a number of proposals, among which was to set up a Commission of Investigation into the events under the 2004 act.
Mr Noonan said consent was an issue in the controversy.
He said the Government was aware of a large number of tapes and the practice was very widespread and had taken place over a very long duration.
He said it ended last November after arising in another court case last summer.
The minister said the existence of one such tape came to attention and the judge in the case decided it was inadmissible in evidence.
Mr Noonan said he understood that Mr Callinan had looked at the issue and the practice was discontinued in November.
He said he presumed that Mr Shatter was informed of this issue by Mr Kenny over the weekend.
He said he understood Mr Shatter did not have prior knowledge of the controversy.
Mr Noonan said events happen and Mr Shatter did not cause them.
He said the country is fortunate to have Mr Shatter as Minister for Justice, whom he described as very competent and at the top of the legal profession.
Revelations not new - Martin
Earlier, Fianna Fáil leader Micheál Martin said the revelations regarding the taping of phone calls in garda stations are not new.
He said he finds it extraordinary the Government is claiming that they are.
Mr Martin said that in a very high profile case in Waterford, where gardaí were convicted in an assault case and which went to the Garda Ombudsman Commission, the practice of recording phone calls was raised in the Ombudsman's report.
He said that report asked the former garda commissioner to consider that practice because the recordings put forward by the Director of Prosecutions in the case were not admissible.
Mr Martin said the Government is giving the impression that this was a new and very serious issue in relation to An Garda Síochána.
He said he was beginning to think the Government was pulling the wool over people's eyes on the matter.