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It "would've been helpful" if Stormont's finance department had done more to assist DETI with sorting out the budget problems with the RHI scheme in June 2015, says Dr McCormick.

Asked if the Department of Finance and Personnel (DFP) had given DETI the necessary help, he says: "I can't see how I can say yes to that.

"I hesitate to blame," he adds, but the finance department's refusal to engage with the Treasury about the issue "definitely didn't help... when something... was going very badly wrong".

Dr McCormick says he "lives with the consequences" of not having asked more questions about the problems with the RHI scheme when it was drawn to his attention in May 2015.

It was originally envisaged that just about £12m would be needed to cover the scheme in the 2014-15 financial year but the cost had almost doubled.

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"I didn't ask hard enough questions at the time... I deeply regret not asking more fundamental questions at the time."

He "assumed" that it was "still fundamentally a sound scheme" at that point and he says that's how it was presented to him by the officials who were working on it.

The witness admits to a "failure on my part" of not having an "instinct" of being more inquisitive at the time.

There was misunderstanding between DETI's energy and finance teams in spring 2015 about the funding arrangement for the RHI scheme.

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In his written witness statement, Dr McCormick says key documents that explained the funding "were not difficult to find" and "most or all of them" had even been "seen and forwarded" between staff in early-2015.

He tells the inquiry that had those papers been dug out they would've "prompted a realisation that the approach had been wrong and therefore we... need to take a new path".

Image source, RHI Inquiry

It was in March 2015 that civil servants became aware that the RHI scheme was running into serious budget problems.

Dr McCormick says the problem should have been drawn to his attention "as soon as the point was clear".

Inquiry panellist Dr Keith MacLean (below) detects a problem within the DETI working culture.

He wants to know if staff were reluctant to speak out because of power struggles or took the view that "it's not my business and if I do say something I'll get my head bitten off for it".

Image source, RHI Inquiry

Dr McCormick admits there may be something to those "very penetrating thoughts and questions".

He says there should be a message of conveying confidence to staff, adding: "Machiavelli said culture is the hardest thing to change."

It is "glaringly obvious" that big concerns about a "grave weakness" in the RHI scheme that were raised by a so-called whistleblower should've been checked out by officials, says Dr McCormick.

Busineswoman Janette O'Hagan (below) contacted DETI numerous times to flag up the unintended overgenerosity of the subsidies on offer, which effectively encouraged claimants to burn more fuel to earn more cash.

Image source, RHI Inquiry

Dr McCormick says he "can't see any defensible explanation" why officials didn't act even when Ms O'Hagan had "pointed out for the third or fourth time precisely the root cause of the problem".

The flaw she tried to draw their attention to was "really quite simple", he adds.

Dr McCormick says that by the time he became involved with the scheme "we were past risk... things had crystallised and had gone wrong".

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"They were no longer risks," they were actualities," he adds.

He accepts that the approach in the civil service to managing risks "clearly hadn't been effective on my watch in time to deal with this".

A risk register was created for the RHI scheme in March 2012 but it was never updated or amended to reflect changes in the project.

It correctly identified possible risks, including the danger of incorrect subsidy levels offered by the scheme, and insufficient budget and suggested ways of mitigating them.

One of the mitigating actions was to closely monitor the risks but that was not carried out.

Image source, RHI Inquiry

Mr Scoffield (above) wants to know why the monitoring did not happen and "simply dropped of the edge of the page".

Dr McCormick says he simply can't see any good reason why nothing was done.

"I can't understand how these clear mitigation measures were not routinely followed through," he says, adding that the temptation is to blame the lack of resources.

The RHI scheme was a "project too far" for officials in Northern Ireland to handle, the head of the civil service told the inquiry in March.

David Sterling (below) also said that if he "had a magic wand we wouldn't have done this".

Those suggestions are put to Dr McCormick, who says he's "not totally sure" he agrees with David Sterling's view.

He believes DETI should've asked "are we capable of taking this on" before it took the leap but he adds that "we didn't ask that question".

"I don't think it's possible to go back in time and answer it precisely so I'm close to what [Mr Sterling] is saying but not just precisely on [his] same point."

Chris Stewart (below) was Dr McCormick's deputy at DETI and the witness is asked whether his post was "too heavily loaded".

Dr McCormick says the policy job was seen within the department was seen as a prime position.

Image source, RHI inquiry

"It was one of the most interesting, most diverse in the civil service," he says.

"I think Chris's post was heavily loaded," he adds, explaining that that was one of the reasons why the responsibilities were redistributed when the department was reformed as the Department for the Economy.

Mr Mills took up his role as DETI's energy boss on the basis that he couldn't work beyond normal working hours due to family reasons.

His predecessor Mrs Hepper had committed far more time to the job that the usual nine-to-five hours and often took work home at evenings and weekends.

Mr Mills was assured that he wouldn't have to do that but the guarantees he was given were not fulfilled and after a year in the job he told a senior manager that the role required someone who "could devote more hours to it than I could".

Dr McCormick acknowledges that he doesn't think the department "did anything" to reduce the workload at the time and was instead focused "trying to keep the show on the road".

The line of questioning turns to the capabilities of Mr Mills (below) and whether he was was "on top of" the RHI scheme during his time running DETI's energy team.

Inquiry panellist Dame Una O'Brien asks how it could not have been clear to to Dr McCormick and his deputy Chris Stewart that Mr Mills "really had as little experience in energy as both of you did".

Image source, RHI Inquiry

The witness replies that as a vastly experienced civil servant Mr Mills was "used to getting up to speed, picking up on what needs to be done".

"I found him convincing, authoritative when I arrived," Dr McCormick adds.

The RHI scheme was set up and run by DETI's energy division, which was a small team with an increasing workload throughout the initiative's lifetime.

The job of leading that team was "seen as a prime post - probably a place to make your name".

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But it was a "challenging" one too, with "extreme demands" on those who held the role.

Fiona Hepper was in the job from the birth of the RHI scheme until late-2013 and John Mills succeeded her at the start of 2014.

One of the key civil service figures in the RHI debacle, Dr Andrew McCormick was the permanent secretary - the top civil servant - at the Department for the Economy, formerly DETI, which set up the energy initiative.

He was in that post at the time when big cracks began to appear in the RHI scheme and he had to clear up much of the mess it created.

His witness statement to the inquiry makes for a dramatic read and you can find it in three parts - here, external, here, external and here, external.

He has since switched roles and now has just as big a task on his hands as he deals with all things Brexit as Stormont's director general of international relations.

And here's a quick fact - his PhD was in isotope geochemistry.

Image source, RHI Inquiry

Dr Andrew McCormick is booked in for an all-day session in the hotseat and he'll be taking questions from the inquiry's senior counsel David Scoffield QC.

BBC News NI

Crucial knowledge about how the RHI scheme operated was lost as officials left the department responsible for running it, said one of Northern Ireland's most senior civil servants.

Dr Andrew McCormick was the permanent secretary at DETI at the time when the major problems arose in the complex energy initiative.

Image source, Pacemaker

He told the inquiry that there was "great regret" that "the baton was dropped" between staff.

He also admitted that it was "impossible to defend" the low staffing level of just one full-time and one part-time official - dedicated to it during that time.

BBC News NI

An independent inquiry into the RHI scandal was established in January last year by the then finance minister Máirtín Ó Muilleoir.

He ordered it in the wake of the huge public concern and what was then a developing political crisis surrounding the scheme.

The RHI Inquiry began in November and Sir Patrick Coghlin (below), a retired Court of Appeal judge, is its chair and has been given full control over how it will operate.

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It will look at:

• the design and introduction of the RHI scheme
• the scheme's initial operation, administration, promotion and supervision
• the introduction of revised subsidies and a usage cap for new scheme claimants in 2015
• the scheme's closure

For more information on the RHI Inquiry, you can read our handy Q&A.

When the scale of the overspend emerged, public and political concern rocketed.

As the minister in charge of the Stormont department that set up the RHI scheme, the DUP leader Arlene Foster faced calls to resign from her role as Northern Ireland's first minister in December 2016.

PA

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She resisted, and Sinn Féin's Martin McGuinness then quit as deputy first minister in protest at the DUP's handling of what had by then become a full-blown political crisis.

That move brought about the collapse of the Northern Ireland Executive. Now, well beyond a year-and-a-half on from that, Northern Ireland remains without a devolved administration.

You can find much more detail on the RHI scheme in our need-to-know guide.

The budget of the RHI scheme ran out of control because of critical flaws in the way it was set up.

Claimants could effectively earn more money the more fuel they burned because the subsidies on offer for renewable fuels were far greater than the cost of the fuels themselves.

At one point the estimate for the overspend was set at £700m if permanent cost controls weren't introduced - temporary cuts have since pulled the budget back on track for now.

Whatever the scale of the bill, it will have to be picked up by the Northern Ireland taxpayer.

The Renewable Heat Incentive scheme - or RHI for short - came to the fore of the Northern Ireland public's knowledge in late-2016... and the fallout from the scandal attached to it is still being felt in the region's politics today.

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The scheme was set up by the Northern Ireland Executive in 2012, as a way of encouraging businesses to switch from using fossil fuels to renewable sources for generating their heat.

Those who signed up were offered financial incentives to buy new heating systems and the fuel to run them.