Northern Ireland senior civil servant believed DUP special adviser 'exerted influence' to keep RHI open
One of Northern Ireland's most senior civil servants believed a DUP special adviser "exerted influence" in keeping the uncapped Renewable Heating Incentive scheme open.
However, Dr Andrew McCormick says has no evidence to substantiate the claim.
Dr McCormick is the permanent secretary for the Economy Department and was the civil service head of the Department of Enterprise.
The adviser concerned has not been named, however, all of the DUP special advisers who could have been involved have stressed that they have not been involved in wrong-doing over the matter.
In a statement to the BBC's Stephen Nolan show, the DUP said: "Prior to December 15 when the BBC broadcast allegations of the involvement of DUP special advisers in preventing the introduction of cost controls for the non-domestic RHI scheme, Dr McCormick had not informed us of the name of any DUP special adviser that he believed to be seeking to offer advice or exert influence over the matter.
"Since the allegation aired on December 15, Dr McCormick has subsequently informed us that it was his understanding that a DUP special adviser who was not the then DETI special adviser was involved in the summer of 2015 but that he had no evidence to substantiate this."
The Renewable Heating Incentive was supposed to help businesses mitigate the costs of running eco-friendly boilers. Unlike a similar scheme in Britain, no cap was initially put on the payments.
The Northern Ireland scheme ended up paying out more than the cost of the fuel - so the more people burned, the more public money they earned. Some applicants were found to heat buildings on an industrial scale just to make money.
It has been revealed that after civil servants urged for the closure of the scheme in June 2015 until a tiered system was introduced in November, there was a spike in applications.
Over a two-and-a-half-year period since its opening up to March 2015 there had been 564 applications.
Between April and September 2015 there were then 359 applications and then in October 2015 there were 429 applications.
The Department of Economy has said the overspend should not exceed £490m.