One other issue that cropped in the evidence from another witness was a dispute between Ms Hepper and a DETI colleague about the administration costs of the RHI scheme.

In December 2012, the department was told by Ofgem that the costs would increase from an earlier estimate of about £1.1m over the first four years to £1.8m.

Ms Hepper said at the time that it was just a "refinement" of the original cost estimate and didn't require review from an internal scrutiny committee.

Image source, Getty Images

But senior DETI finance official Trevor Cooper's view was different - he told the inquiry there was "no doubt" that it should've gone back to the committee he chaired for consideration..

An accommodation was reached that Ms Hepper would then make a submission to Mr Cooper and another committee member, outlining the details of the changes - they confirmed that they were content with them.

She tells the inquiry that the issue was "resolved quite quickly", and the committee members felt it didn't need further consideration from Stormont's finance department.

Sir Patrick says that not only is there no record of the meeting with Mrs Foster but Ms Hepper cannot remember whether it was by telephone or face-to-face meeting.

He queries how, if it was a phone conversation, an issue of that nature could be explained "to such an extent it would enable the minister to make an informed decision".

Image source, RHI Inquiry

Ms Hepper says she went through all the options "and there was nothing hidden from the minister".

She believes there was "absolute clarity".

Civil service guidance states that "at least 48 hours" should be given for a minister to consider a decision, even in the case of those thought to be urgent.

Mr Scoffield asks whether the "practice of going to see the minister or asking for something to be considered urgently" was something that was "widespread" within DETI's energy division.

It wasn't widespread, says Ms Hepper, but there were specific occasions where it had to happen.

Image source, Getty Images

The guidance also states in bold that it is the responsibility of the division to record meeting minutes - in the case of the RHI scheme, that would have fallen to the energy division to do.

Time and time again minutes of meetings about the scheme have been found not to exist.

Ms Hepper says that "over time, as things got busier and busier" staff took "action points" rather than more detailed minutes, and it was "not unusual" for there to be no official note of meetings.

Inquiry chair Sir Patrick Coghlin says he is trying to "clarify the quality of civil service decision-making" about the RHI scheme.

The Department of Energy & Climate Change (DECC), which was running the similar initiative in Great Britain, decided to put cost controls in place even though uptake on its scheme was low and it believed the measures were unlikely to be needed.

Image source, Getty Images

DETI was informed of that move, and Sir Patrick says he find it "very difficult to understand" why the Stormont department didn't put that information in writing for the minister "who ultimately would have to take responsibility for the decision".

He says it should have been "straightforward... procedure for the civil service in "dealing with public money".

Ms Hepper says that simply discussing the issue with the minister at the time "seemed appropriate" but "with hindsight" she accepts that putting that key detail in writing would've been a better approach.

In mid-2012, RHI scheme administrator Ofgem warned DETI not to go ahead with the scheme without adopting cost controls similar to those adopted in the Great Britain RHI initiative.

Ms Hepper met Mrs Foster after the Ofgem warning.

The minister has told the inquiry she has no recollection of being clearly informed of the risks of proceeding without cost controls, and that if the issue had been raised "Ofgem's warning's must have been significantly downplayed".

Image source, RHI Inquiry

She also said that if she had been presented with such a significant issue she would have asked for a formal submission from her officials.

That, Mr Scoffield says, contradicts Ms Hepper's earlier evidence that the matter was fully discussed and the minister was made aware of the risks.

Ms Hepper says she has a clear recollection of the meeting, adding: "I don't believe it was downplayed in any way."

Another point at which the accounts of Mrs Foster and Ms Hepper differ is in May and June 2011.

A submission to the minister outlining the details of the two options for the RHI scheme had been based in a draft report by external consultants, but when their final report was received a month later, the projected costs of the two options had changed dramatically.

The cost of the ongoing subsidy scheme - which was eventually adopted - was estimated to cost more than £100m more than it had done in the report the previous month, and that meant it cost significantly more than the other option, the up-front grant scheme.

Image source, RHI Inquiry

Mrs Foster decided to go for the subsidy option on the basis of the draft report

The former DETI minister has said she would've "expected officials to draw any significant or material changes affecting my prior decision... directly to my attention", adding: "This was not done."

Mr Scoffield says that is at odds with Ms Hepper's view, which was that it was her expectation that the minister or her adviser should have looked at the report and raised any issues with the energy team.

Ms Hepper accepts that what the minister has said "is factually correct" and the energy team did not include that crucial detail in the submission to her.

No note was taken of the meeting with Mrs Foster and inquiry chairman Sir Patrick Coghlin is not impressed.

He asks whether the lack of clarity on what was said underlines "the need for a memorandum or note, either by you, by her, by a private secretary".

Image source, RHI Inquiry

Ms Hepper accepts that and says that "big lesson" is something "we will take away from this".

"Not very good public policy, is it?" says Sir Patrick.

In her written evidence to the inquiry, Mrs Foster has said in that a submission she received from her department's energy team in June 2011 led her to believe that an ongoing subsidy scheme model the "highest potential heat output at the best value" for the RHI scheme.

It was one of two options up for consideration, the other being an up-front grants scheme that was in fact the better value option but which was ultimately rejected.

She has also said that having reread the documents she was given at the time it it "appears clear to me" that the ongoing subsidy option was being recommended to her by her energy team and a consultancy firm that drew up the framework for the scheme.

Image source, Reuters

Mr Scoffield says that "contrasts" with evidence Ms Hepper provided when she said she expressed no preference and left it up to the minister to decide.

Ms Hepper says she stands by what she said, telling the inquiry that she has a "clear recollection" of the meeting she had with the minister at which the issue was discussed.

"I would hold to the information that I provided to the inquiry under oath," she adds.

The inquiry's senior counsel David Scoffield QC kicks off today's session.

Image source, RHI Inquiry

He says he wants to tidy up some loose ends concerning Ms Hepper's earlier evidence before progressing to the operation of the scheme from November 2012 to late-2013.

Mr Scoffield says the inquiry is particularly interested in two meetings Ms Hepper had with the then DETI minister Arlene Foster in June 2011 and mid-2012.

BBC News Northern Ireland

The civil servant who largely ran the RHI scheme told the inquiry that ministers should be more fully involved in policy-making in Stormont departments.

Image source, RHI Inquiry

Peter Hutchinson made the remarks as he concluded his evidence - almost a full five days of it - to the inquiry.

He was the only full-time member of staff running the complex subsidy scheme and said there were many lessons to be learned from the debacle.

BBC News Northern Ireland

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.

Image source, Pacemaker

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 Democratic Unionist Party (DUP) leader Arlene Foster faced calls to resign from her role as Northern Ireland's first minister in December 2016.

Image source, PA

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, more than a year 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.

The most recent estimate for the overspend was set at £700m, if permanent cost controls aren't introduced.

The massive overspend bill 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 autumn 2016.

Few people, if anyone, would have expected it to have the consequences it has done in the months that followed.

It 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.

Thanks for joining us for our live coverage of the Renewable Heat Incentive Inquiry from Stormont's Parliament Buildings.

It's damp and and gloomy on the hill this morning - a wee bit dreich, if you prefer the Ulster-Scots.

After former Department of Enterprise, Trade and Investment civil servnt Peter Hutchinson's two days in the witness chair this week, we'll hear from his ex-boss Fiona Hepper today.

She's been before the inquiry before but has more questions to answer today and tomorrow, and you can follow it all with us here.