Sinn Féin deputy leader Mary Lou McDonald has portrayed a Fine Gael and Fianna Fáil coalition as the "nightmare scenario" for anyone who believes in equality.

Responding to the latest opinion polls, which some commentators suggest point to such a combination, Ms McDonald claimed there was not “a whit of difference” between them and also asserted both disregarded low and middle income families.

“If you believed everything that went before is okay - bad decisions and bad governance - then Fianna Fáil and Fine Gael are your only man.”

Ms McDonald, when asked about the appreciable drop of support for her party in the weekend opinion polls replied: “Too many opinion polls makes for hormonal politics. You are up. You are down. You are in. You are out.”

Referring to the testy exchange with a man on Grafton Street last week who claimed the party opposed anybody who aspired to earn over € 70,000 per year, Ms McDonald claimed the import of that was the traditional ruling class were back in business.

She said she accepted the man was a concerned citizen and was entitled to give his view.

“He was a concerned citizen who happened to work for ACC bank at one stage, she said and added he now worked for a large financial interest.

She said he did not make his background plain when talking to her but added she did not have an particular issue with that.

“My strong sense is that the insider class may take a cue from [that encounter],” she said.

Ms McDonald was speaking at a Sinn Féin conference on political reform held at party headquarters in Parnell Square, Dublin.

The Dublin Central TD also criticised Taoiseach Enda Kenny's remarks on 'whingers' notwithstanding his apology earlier on Monday.

“I myself think he is a bit of a whinger and I have endured his whinging for five years,” she said.

He thinks if you are critical of his government and if you have been let down by the health services or housing policy, or toss and turn at night over household bills, you are a whinger.

“I don’t see it that way. I think those people are heroic,” she said.

"Enda Kenny should stop his whinging and he should get real."

Ms McDonald rejected the assertion Sinn Féin has no prospect of going into government because it had ruled out any alliance with Fianna Fáil or Fine Gael.

Asked how it could make up the numbers she said it was not only Sinn Féin but the larger ‘Right 2 Change’ group which was fielding over 100 candidates.

Asked would Gerry Adams be Taoiseach in the event of that alliance somehow securing sufficient seats, she replied: "We have not gone so far as to discuss who the Taoiseach might be."

She said that all members of the group were receptive to being in government and all had signed up to a willingness to serve in government. She said they would have to cross the Rubicon first to see how that would transpire.

Ms McDonald was asked about the contradiction between Mr Adams and the Stack family and their denial that they supplied him with names of those responsible for the 1970s murder of their father, Brian Stack, a senior prison officer in Portlaoise.

Ms McDonald said she had not spoken to Mr Adams about this issue.

“What happened was awful for that family. It should not have happened. I feel desperately desperately sorry for them.

Their heartbreak and anguish must exist to this day.”

She repeated the Sinn Féin line that anybody with information on the case must go to the Garda Síochána. She also said she was sure that any information Gerry Adams had had been passed on.