The “political establishment” is “desperately reaching for any excuse to exclude Sinn Féin” from government, party leader Mary Lou McDonald has said.

Ms McDonald was answering questions on RTÉ Radio 1 about revelations relating to the “cash for ash” inquiry in Northern Ireland, including that Máirtín Ó Muilleoir, during his tenure as the Sinn Féin finance minister, had sought the permission of senior republican figures in Belfast before he agreed to bring the controversial scheme to an end.

The claim has been cited by both Fine Gael and Fianna Fáil as evidence that Ms McDonald is not wholly in control of her party, but is obliged to take the views of senior former IRA figures into account.

On the basis of these concerns, both big parties have said they will not contemplate a coalition government with Sinn Féin.

Simply consulting the party She said Mr Ó Muilleoir was simply consulting with the party before making a decision on the cash for ash scheme.

She insisted she would not take instructions from anyone in the party, but would “take advice and good counsel”.

A referendum on Irish unity was “a bottom line for all of us” in the event she were to become involved in forming a government, she said, adding that a “forum or citizens’ assembly” to discuss the issue should happen “sooner rather than later”. After that, she said, a five-year window is appropriate for calling a referendum”.

She emphasised her willingness to reach out to unionists to discuss a united Ireland, but said that in a 32-county state she did not believe there should be official commemorations of the RIC or the RUC.

Retirement age Ms McDonald pledged that if Sinn Féin were in government it would restore the retirement age to 65, at a cost of €365 million. She said the idea that people would be forced to work after 65 was “indecent”.

Asked about the demographic pressures that are seeing pension ages increase in western countries, Ms McDonald said that if young people were given access to housing “the demographics will take care of themselves”.

Ms McDonald declined to say whether she would be a candidate for taoiseach when the new Dáil meets, but said her focus would be on delivering a “republican programme for government”.