Tánaiste Frances Fitzgerald is under intense pressure on Tuesday from her Fine Gael colleagues to resign in the wake of fresh revelations about the treatment of Garda whistleblower Sgt Maurice McCabe.

The release of emails about the controversy yesterday evening undermined efforts to defuse the row between Fine Gael and Fianna Fáil over the Tánaiste which has brought the State to the brink of a general election.

The Department of Justice emails show that Ms Fitzgerald was repeatedly told in 2015 about an “aggressive” approach to undermine Sgt McCabe at the O’Higgins commission, which examined allegations of garda malpractice.

The Tánaiste last night tweeted that she could not interfere in the O’Higgins commission and that she looked forward “to giving my evidence” in January to the Charleton Tribunal, which is now looking into an alleged smear campaign against garda whistleblowers. Ms Fitzgerald’s spokeswoman said her position had not changed.

Tánaiste Frances Fitzgerald pictured at Government Buildings last evening. Photograph: Cyril Byrne

There was mounting anger from within Fine Gael in the wake of the emails last night as Taoiseach Leo Varadkar held a late meeting with Fianna Fáil leader Micheál Martin.

Although the Government spokesman insisted that the revelations had not changed Fine Gael’s support for Ms Fitzgerald, her party colleagues said they had defended the Tánaiste over recent weeks in the hope that further embarrassing details would not emerge.

1/2 As Justice Minister I could not interfere with the O'Higgjns Commission. This is confirmed twice in today's docs & has been confirmed by the AG. — Frances Fitzgerald (@FitzgeraldFrncs) November 27, 2017 2/2 The Tribunal will objectively judge the appropriateness of my conduct. I look forward to giving my evidence to the Tribunal early in January. — Frances Fitzgerald (@FitzgeraldFrncs) November 27, 2017

Email threads discovered in search of records

One minister said they were defending her on the basis of something which had now proved to be “untrue”. One deputy said it seemed as if it was “game over” for her and expressed concern that Mr Varadkar “didn’t intervene” to avert the crisis before the latest details emerged.

Another Minister said Ms Fitzgerald had already “lost ground” within the parliamentary party over the weekend as voters and the Fine Gael organisation reacted angrily to the prospect of a pre-Christmas election.

“The mood has darkened, but the Taoiseach has just expressed full confidence in her. Damage is done now at this stage,” said the Minister.

While both parties had been inching towards a compromise, the controversy took a turn for the worse after the release of the emails.

Ms Fitzgerald, who was minister for justice at the time of the emails, had told the Dáil last week that she only learned of the approach at the tribunal in 2016 in media reports.

However, the emails show senior officials requesting Ms Fitzgerald be notified about the matter and her private secretary confirming that she had “noted” the email’s contents.

The emails also show that the department discussed and co-ordinated with the gardaí a response to queries from RTÉ about the approach to question Sgt McCabe’s motivation at the commission.

In two separate emails on July 4th, 2015, the Tánaiste was advised of media queries about the “aggressive” approach being adopted by the former garda commissioner Nóirín O’Sullivan and advised how to respond if the media ask her about the matter.It was a senior Department of Justice official who described the approach as “aggressive”.

The emails reveal that a senior official suggested to Ms Fitzgerald that she should say that it would be “very unfair to Sgt McCabe” if she was to respond to queries about the commission.

The suggested responses were also sent to Ms O’Sullivan, who had also forwarded the Garda Press Office’s responses to the Department of Justice, indicating a degree of co-operation between the department and the gardaí in dealing with the issue.