Arlene Foster's former special adviser was named yesterday as the DUP figure who influenced a decision to keep the controversial Renewable Heat Incentive scheme open.
In an intense and dramatic question and answer session with the Public Accounts Committee, senior civil servant Dr Andrew McCormick revealed he believed DUP man Dr Andrew Crawford was behind the decision to keep the initiative up and running longer than it could have been.
He added he had no specific evidence to support his claim.
The revelation, which came at the insistence of PAC chair Robin Swann, will send shockwaves through Stormont, as Dr Crawford was former First Minister Arlene Foster's adviser at the time she was Enterprise Minister and set up the scheme in 2012.
Dr McCormick said he believed Dr Crawford was exerting influence on his successor, DUP special adviser Timothy Cairns, at the time discussions were under way to impose caps on the scheme in 2015.
He said Mr Cairns forcefully set out reasons the initiative should carry on without caps for an extended period at a meeting that August, and in the end, he got his way. Dr McCormick added that he believed in turn, Mr Cairns had come under pressure from Dr Crawford behind the scenes, although he had no evidence to prove his suspicions.
Dr Crawford denies the allegation.
It was during this extended period, between October 1 and November 17, 2015, that the now well-known spike happened, forcing the cost of the botched scheme to rocket.
However, the Economy Department official insisted that, to his knowledge, Mrs Foster followed the advice of her officials throughout the process and was not advised at any point she needed to take control of costs. The reason, he said, was because at the beginning of the scheme, when Mrs Foster was in the department, uptake was slow.
In another crucial revelation, Dr McCormick claimed 'insider information' may have played a part in the 'cash for ash' scheme, which could cost the public purse as much as £490m. Dr McCormick said he believed figures within the renewable heating industry had been informed 'prematurely' about planned cuts to the scheme, which was paying out £1.60 for every £1 spent by users, and had pushed for it to be kept open.
He said: "The consequence is very serious, because this shows that there was premature awareness of the potential for the tariff to be reduced and the message went within the sector - get in quick." He also said people within the industry were saying to others in the political class "we hear something is about to happen, can you do something about it and can you give us longer?"
That 'premature' information may have come from officials, he added, although again he said he had no evidence of this.
During his evidence to the PAC, Dr McCormick, Permanent Secretary for the Department of the Economy, also revealed he knew of at least one matter linked to the RHI scheme that energy watchdog Ofgem has discussed with the PSNI.
Dr McCormick also apologised on behalf of the civil servants overseeing the scheme, admitting they had failed to spot its major flaws.
In a statement issued by the DUP last night, Dr Andrew Crawford said: "As someone who worked in DETI for many years, I spoke to the then DETI Special Advisor ('spad') at that time about the RHI scheme.
"Any discussions with the DETI spad during the summer of 2015, would have been on the basis of my experience of the department.
"In discussing the matter with the DETI spad, I would have been offering informal advice and assistance as a colleague to my successor in the department and not on behalf of the Finance Minister or the party.
"However, as I pointed out to the BBC in December, I did not attempt to keep the RHI scheme open at the original tariff against the wishes of the Minister.
"Indeed, I specifically stated on July 31, 2015, that the department, 'will need to make changes from October 1'."
Dr Crawford, the son of a farmer from Beragh in Co Tyrone and former employee of the Ulster Farmers' Union, earlier revealed his poultry farmer brother is a recipient of the RHI scheme.