First Minister Arlene Foster has faced fresh calls to stand down following new revelations over her role in a bungled heating scheme.
Mrs Foster rejected calls on Monday from Opposition parties for her to resign over the deeply flawed Renewable Heating Incentive scheme, which could leave taxpayers picking up a £400m bill.
However, UUP leader Mike Nesbitt said Mrs Foster is “in denial” and is “blaming everyone but herself”, comments echoed by SDLP leader Colum Eastwood.
And on Tuesday, Mr Nesbitt kept the heat on the first minister, claiming his party had “uncovered proof” that the she had played a key role in bringing about the financial debacle.
He said that Mrs Foster, who was in charge of DETI when the scheme was rolled out, had chosen not to adopt a vital cost control measure.
So-called degression procedures, which were applied to the successful RHI scheme in GB, meant that as more people applied, the tariff would reduce, ensuring the scheme would not go over budget.
Mr Nesbitt claimed Mrs Foster’s decision not to adopt this crucial safeguard in the local RHI scheme was a fatal error, leading to a deluge of applications which eventually broke the budget.
He added: “At a meeting of the then enterprise trade and investment committee at Stormont, an official was questioned about the reason why Northern Ireland did not adopt the so-called degression procedures.
“At the meeting on February 9, 2016, the official said degression was discussed in the context of the department’s intention to introduce a domestic RHI scheme. He went on to state: ‘So the minister decided that the priority should be on the introduction of the domestic RHI scheme’.
“Here for the first time is proof that Mrs Foster’s fingerprints are on the decision-making process.
“It is time Mrs Foster stopped blaming others and embraced the age-old principle of ministerial responsibility. She was not only aware of what was happening, she was making it happen.
“So, now there is a smoking gun, the public will ask what is more important to Mrs Foster – her job or the reputation of the devolved institutions?”
In response to Mr Nesbitt’s claims, DUP MLA Christopher Stalford told the News Letter: “Notably a few short weeks after these ‘smoking gun’ comments were made, Mike Nesbitt and his colleagues voted against the closure of the renewable heat scheme.
“In Mike Nesbitt’s endless search for a headline he conveniently ignores the underspend during each of those early years of the renewable heat scheme.
“No proposals for cost control were brought forward to Arlene Foster at any time.
“Not only were the UUP opposing the closure of RHI but putting forward an argument that tariffs were not high enough. Perhaps Mike Nesbitt is so obsessed with a ‘smoking gun’ because he hopes it will obscure his party’s record.”
The RHI scheme was fundamentally flawed, as it paid out more than the fuel cost, meaning users who burned fuel unnecessarily would actually earn money.
A Stormont committee is to convene a special meeting on Thursday to consider whether to call the first minister to give evidence on her role in the scandal.
The Assembly’s Public Accounts Committee is currently investigating the RHI furore.
Ministers do not usually appear before the PAC under Assembly conventions but, such is the scale of the fall-out from the RHI, its members are to discuss a proposal from SDLP MLA Daniel McCrossan that Mrs Foster gives evidence.
The first minister, who has been accused of not doing enough to pursue whistleblower allegations that sought to expose flaws in the system, has indicated a willingness to answer questions on the matter.