Sinn Féin is calling for an independent panel to investigate Northern Ireland’s botched Renewable Heat Incentive (RHI) scheme.

The party set out the details on Friday of what it believes an independent investigation into the controversy should look like - just as First Minister Arlene Foster issued another defiant riposte to her critics.

Ms Foster, who has repeatedly rejected calls for her resignation, posted an image on Facebook on Friday of a guinea pig wearing a pair of pink love-heart shaped glasses below the phrase: “Can’t see all the haters when I’ve got my love glasses on.”

The post attracted criticism from her political opponents, with Alliance leader Naomi Long saying: “They’re not haters, they’re taxpayers. And angry ones at that.

“We’re in the teeth of a political and financial crisis, much of it of her making, and the First Minister opts for this by way of a response to her critics?

“Let’s hope love glasses also work for people lying on trolleys, waiting on cancer drugs, suffering benefit cuts, struggling to pay their heating and food bills, eh? Because it’s all just a £500 millioni joke, right?”

Ms Long continued: “I was excoriated for suggesting the DUP were even more arrogant and beligerent under Arlene Foster than Peter Robinson. I think even he would have balked at donning ‘love glasses’.”

Earlier, Northern Ireland’s Justice Minister accused the First Minster and Deputy First Minister of letting her down over the “cash for ash” controversy but she said she did not believe Arlene Foster should step aside from her role.

Claire Sugden, the independent unionist MLA, who forms the Stormont Executive with the DUP and Sinn Féin, says they have “reverted to party politics” over the RHI scheme but denied they see her as a “soft touch”.

Sinn Féin’s draft terms of reference were given to the DUP and civil servants on Wednesday after it rejected proposals by the head of the civil service.

Sinn Féin believes its proposals will “get to the truth in an independent and transparent way” and that Ms Foster must step aside from her role during the preliminary investigation into the scandal which is expected to cost to the Northern taxpayer around £490 million.

A Sinn Féin source told The Irish Times the party does not believe The Inquiry Act of 2005 is the way to proceed at this time as it could allow for a minister to interfere with the independence of an investigation, and gave as an example of its limitations the family of murdered solicitor Pat Finucane rejecting this type of probe into his death.

The Sinn Féin source says the RHI investigation had to be “independent, time bound and cost effective”.

The party is proposing that a minister establishes an investigation but it is then handed over to the attorney general to appoint a judicial figure to chair, who would then set the terms of reference and appoint an expert panel.

This would not preclude having sessions in public.

Sinn Féin says compellability of witnesses and documents has been central to its demands and that a new piece of legislation could be progressed through accelerated passage in a matter of weeks.

Final report

Sinn Féin suggests a preliminary RHI report could be produced within four weeks and a final report within three months.

Earlier, Northern Ireland’s Justice Minister accused the First Minster and Deputy First Minister of letting her down over the “cash for ash” controversy but she said she did not believe Arlene Foster should step aside from her role.

Claire Sugden, the independent unionist MLA, who forms the Stormont Executive with the DUP and Sinn Féin, says they have “reverted to party politics” over the RHI scheme but denied they see her as a “soft touch”.

Earlier Ms Sugden broke her silence on the ongoing crisis with a Radio Ulster interview.

“Martin and Arlene have both let me down,” she said of the First Minister and Deputy First Minister respectively.

The East Derry MLA said her position on the overgenerous green energy scheme had not changed since before Christmas and that she had been busy doing her job.

She described RHI as “a cross-cutting issue” rather than a justice issue and claimed she does not have the power to unilaterally set up a public inquiry into the matter and that it would need the Stormont Executive’s backing.

“People saying I have unilateral power on initiating a public inquiry are misinformed,” she said.

Ms Sugden was critical of Ms Foster and Mr McGuinness but says she will not resign and does not support calls for a fresh Assembly election.

Public inquiry

On whether she could support a Sinn Féin motion calling for Ms Foster to stand aside from her role as First Minister, she said she could support an independent investigation into RHI but was concerned a public inquiry could be lengthy and expensive.

However she said it would be unfair to Ms Foster to force her to stand aside and that she was in “two minds” over whether she could support Sinn Féin on this element of its demands as she was “unsure what it would achieve”.

“Essentially that is punishment without proper, fair investigation,” she said.

“Until we can do that (an investigation) I don’t think that is fair.”

Foyle’s People Before Profit MLA Eamonn McCann believes Ms Foster should resign as First Minister and that Ms Sugden should consider her position rather than act as a “linchpin” for the Stormont Executive “if it is not delivering truth and justice to the people”.

Stormont is currently in recess and is expected to reconvene on January 16th.