RHI scandal: Pressure mounts for RHI public inquiry
The UUP and SDLP have called on First Minister Arlene Foster to step aside while a former DUP minister's claims over a flawed energy scheme are probed.
Overgenerous offers of fuel subsidies meant the Renewable Heat Incentive (RHI) scheme went vastly over-budget.
Jonathan Bell said top DUP advisers stopped him from ending the scheme that could cost the public an extra £400m.
Mrs Foster has denied any wrongdoing in the scandal, and said she will not resign over her role in the initiative.
- BBC News NI reports on 'cash for ash' scandal
- Advisers' 'pressure' stopped scheme closure
- Reaction to Jonathan Bell's RHI revelations
- Q&A: What is the RHI scheme?
- Timeline: RHI scheme scandal
- How does RHI £400m overspend add up?
The RHI scheme was set up by the Department of Enterprise, Trade and Investment (Deti) under the stewardship of Mrs Foster in 2012 to encourage businesses and other non-domestic users to move from using fossil fuels to renewable heating systems.
But flaws in setting the scheme's subsidy rate left it open to abuse as claimants could earn more cash the more fuel they burned.
About £20m a year for the next two decades could be taken from the Northern Ireland budget to cover the overspend.
In an interview with the BBC's Stephen Nolan, Mr Bell, a former enterprise minister, broke ranks with his DUP colleagues and made a number of sensational claims about how the controversial scheme was handled.
Analysis: Mark Devenport, BBC News NI political editor
"Cui bono?" The old Latin question about who stands to gain needs to be asked again and again.
While the blame game is necessary and inevitable, no-one must lose sight of the fact that Stormont is committed to paying out for this scheme for the next 20 years.
Those contracts must be re-examined in order to see if the "too good to be true" deal can be renegotiated.
He claimed that senior DUP aides "intervened" to stop him from cutting the lucrative subsidy offer in autumn last year.
The DUP MLA also alleged that attempts were made "behind my back" by special advisers to remove references to Mrs Foster and her department from documents relating to the scheme.
The advisers have denied Mr Bell's claims and said their role is simply to advise, not to influence decisions.
The DUP hit back at Mr Bell on Friday, describing his claim as a "ham-fisted diversionary tactic" to distract from the "fact he, as minister, made the crucial and catastrophic decision to delay RHI cost savings".
Sinn Féin, the DUP's partner in the Northern Ireland Executive, has said there should be an independent investigation.
The party's Finance Minister, Máirtín Ó Muilleoir, said it should look at "why this debacle went ahead, but, in particular, who benefitted".
He added: "We need to get to get to the facts and the truth - I think we'll only get to that through a high-level investigation and that needs to happen urgently."
Ulster Unionist leader Mike Nesbitt said the integrity of the Stormont intuitions has been left "in the gutter of public opinion" by the scandal and he called on the first minister to stand down.
He said that all of the paperwork linked to the RHI scheme should be published, adding: "If ever there was a time for total openness and transparent, it is today."
The Northern Ireland Assembly's Public Accounts Committee is already examining the scheme's failings, and Mr Nesbitt said the DUP aides should appear before it.
His call for Mrs Foster's resignation was echoed by his SDLP counterpart Colum Eastwood, who plans to table a motion of no confidence in the first minister at the assembly on Monday.
It calls for her to be excluded from office for six months.
"The only way we can find out the truth now is if all the documents that have been referenced to are put into the public domain," Mr Eastwood said.
"We are now in the realm of some sort of a public inquiry - the public desperately need some confidence put back into our institutions."
Alliance Party leader Naomi Long said a judge-led inquiry would be "the best way to uncover the truth on behalf of the public."
"We need to know why the scheme was kept open after the financial implications were known and who benefitted," Mrs Long added.
"At the very least, the first minister should step aside for the duration of that investigation and all correspondence should be released publicly."
However, TUV leader Jim Allister said he doubted whether such an inquiry would be established.
"I think in normal society a [judge-led inquiry] is what would be expected, but I'm not sure that we will get that," he said.
The first minister said Mr Bell "took all the decisions" in relation to the scheme during his time as minister.
When Mrs Foster was enterprise minister, a whistleblower raised concerns about the flaw in the RHI scheme, but they were ignored by Deti officials.
Mrs Foster has since said that civil servants did not tell her of any issues arising from the whistleblower's alert.
The RHI scheme was finally halted early this year, by which time its overall cost had reached £1.18bn.
The Treasury, which was due to cover the cost of the scheme, said the executive would have to find the money for the enormous overspend.
But Mrs Foster said that the executive believes at least half of the scheme's projected £400m cost to the Stormont budget can still be saved.