Inquiry counsel Mr Aiken calls it a day after an afternoon of highly-technical questioning, compounded by a lack of documentary evidence coming from Mr Stevenson's direction.

There are still questions for the witness to answer, so he'll have to come back this week.

Join us again at 09:45 tomorrow for evidence from two new witnesses - Nicola Wheeler of the Departmental Solicitors Office and Alan Bissett, formerly of Arthur Cox solicitors.

Time for us to wrap up and head out into the Stormont darkness... have a good evening!

BBC News Northern Ireland

Former Stormont enterprise minister Arlene Foster will be called to give evidence to the RHI Inquiry earlier than expected, it emerged.

Image source, Reuters

Before she went on to become first minister and DUP leader, Mrs Foster oversaw the department that introduced the flawed green energy scheme.

She had not been due to testify until later this spring but inquiry chairman Sir Patrick Coghlin revealed this morning that she would be asked to give evidence at an earlier date.

A letter from DFP's supply team - of which Mr Stevenson was a part - to DETI confirming the approval of the RHI scheme approving exactly replicated suggestions by a finance department economist.

Both the supply team and the economists were to give their individual assessments of the scheme.

Image source, Getty Images

But Mr Aiken points out that five bullet points in the approval letter that raised issues to be addressed were "direct lifts" from material provided by economist Stuart McAllister and are not accompanied by any additional material from the supply team.

Asked if that is unusual for a copy-and-paste job like that to happen and whether the supply team relies on the economists' views.

Mr Stevenson is "not surprised" by it but says it "always surprised me" how often the supply team and economists "had similar views" on projects.

Mr Stevenson says he has personally searched for the documents detailing his role in the RHI scheme business case process but "to date we're not able to turn anything up".

Inquiry panellist Dame Una O'Brien wants to know whether there are documents relating to the other business cases Mr Stevenson was dealing with at the time.

Image source, Getty Images

If documents from other cases are missing that would suggest there's a theme of not saving them, she says, but if it's only RHI-related documents that are missing that would "suggest something entirely different".

Mr Aiken says one interpretation is that Mr Stevenson wasn't involved in the RHI scheme as much as he thinks he was.

Mr Aiken says the panel will have a problem because of a lack of documentary evidence relating to Mr Stevenson's involvement in the RHI scheme business case process.

Mr Stevenson indicates in his written evidence that he didn't have time to save emails in the civil service electronic archive, or to follow up telephone calls with emails.

Image source, RHI Inquiry

Instead, he says he would usually have saved relevant emails to a folder which would be passed to the admin team to add the documents in the system.

Mr Aiken puts it to Mr Stevenson that "somebody hasn't done something that they should have done".

"Absolutely, I suspect that is the case," says Mr Stevenson.

Finance Department officials would often "come under pressure for a quick decision" to approve projects, says Mr Stevenson.

Image source, RHI Inquiry

That was a "point of conflict" between DFP and other departments, he adds, and the officials tried to resist rushed requests.

He says his boss Jack Layberry tried to establish a culture at DFP of rejecting such approaches - a common phrase he used was: "If a department is looking for a quick decision then the answer's 'no'."

One theme we've seen in the inquiry so far is the significant workload faced by some civil servants.

Mr Stevenson is another who had plenty in his in-tray, suggesting that his post was "fully-loaded" and he had a heavy volume of work to deal with.

Image source, Getty Images

During the time when he was dealing with the business case for the RHI scheme, Mr Stevenson also had eight others to process within a three-week window.

Among those were the Irish Open golf tournament and a festival marking the centenary of the Titanic's sinking.

He says that some of the projects that "appear small in nature" were of "key strategic importance" to the Northern Ireland, and the "value doesn't tell the full story".

This afternoon's witness Stuart Stevenson was a supply officer with the Department of Finance and Personnel at the time when the RHI scheme was set up.

Image source, RHI Inquiry

The inquiry's junior counsel Joseph Aiken runs through Mr Stevenson's background and the work of a supply officer.

You can find Mr Stevenson's written statement to the inquiry here, external.

Image source, Getty Images

That's all from Ms Hepper for now - she has answered all of the questions the inquiry has for her about the first phase of the RHI scheme, but she'll be back another time to discuss its latter stages.

We'll be back at 14:05 to hear from Stormont finance department official Stuart Stevenson - join us then.

Inquiry panel member Dame Una O'Brien (below) draws Ms Hepper's attention to another line in Mr Harnock's email to his Ofgem colleagues.

He describes Ms Hepper's response to news of an increase in Ofgem's admin costs, saying that she was "furious about not being told about this matter earlier".

Image source, RHI Inquiry

Dame Una is concerned about DETI's relationship with Ofgem, observing that it is "very unusual to see in the world of government departments relating to other public sector bodies people minuting in this way".

Ms Hepper says DETI had "a very good working relationship with Ofgem" but her anger was in the context of an increase from £368,000 to £700,000 "without a good rationale".

Mrs Foster was "adamant" that the RHI scheme should begin in October 2012, according to Ofgem.

Image source, RHI Inquiry

In an email to his Ofgem colleagues in August that year, Matthew Harnock says he was told by Ms Hepper about the DETI minister's position.

Ms Hepper says it is true that Mrs Foster had given a specific indication to that effect.

Without interim cost controls in place it would not be possible for the RHI scheme to be suspended mid-year.

But Sir Patrick puts it to Ms Hepper that the committee had been told that the scheme could be suspended in that way.

He asks whether, in the light of the decision not to adopt cost controls, Ms Hepper should have gone back to the committee to inform them that a mid-year suspension would not be possible, and he suggests that the information it was given "was not accurate".

Image source, RHI Inquiry

Ms Hepper says that if necessary "we would have had to change the regulations - we made that quite clear to the committee".

Sir Patrick wants to know whether it was made clear to the committee that regulatory power would have been required to stop the scheme.

"Maybe the detail isn't in the minutes but that's the only way it could be stopped," Ms Hepper says.

Ms Hepper says she told Mrs Foster "all the detail" about Ofgem's advice and at what stage the RHI scheme was at at that time during their phonecall.

Image source, Getty Images

"She was content [to launch the scheme] on the assurance that we would be bringing forward the consultation [on adding cost controls] the following spring/summer and bring it into play," she adds.

"She would've had all the information."

And Ms Hepper says the decision to proceed was "a balanced enough" one on the evidence the department had.

Ms Hepper says she felt that Ofgem's warning not to proceed with the scheme as it was was "sufficiently important" to "raise it further up the line".

But she adds that Ofgem officials she was dealing with were "content" with DETI's plan to add the cost controls at a later stage.

Image source, Getty Images

She says she spoke to the then minister Arlene Foster, probably on the phone that echoes a point in her written witness statement, in which she says: "I do not believe there was a written submission to the minister."

Mr Scoffield asks why it wasn't put on paper, given that this was a "significant" issue.

Ms Hepper says the intention was to "get a word with the minister as soon as we can" and it wouldn't have been unusual for things to be done that way.

Ofgem suggested that DETI should hold off on introducing the RHI scheme so it could include in the regulations some of the changes being adopted in the GB initiative, including cost controls.

Ms Hepper says there was a commitment with the then minister Arlene Foster (below) to get the scheme lunched in September 2012.

Mr Scoffield wants to know if this commitment was recorded, asking: "Where can we find it?" he asks.

Image source, Reuters

Ms Hepper says "it was probably in discussions with the minister".

A change of the type recommended by Ofgem would have required 12-week consultation, and the preparation of new regulations that would have to be passed by the Northern Ireland Assembly's Enterprise Committee, she says.

This would have pushed back the launch until "at the earliest February or March of 2013".

BBC News Northern Ireland

Away from Stormont, it's been confirmed that Northern Ireland Secretary James Brokenshire has resigned.

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It's understood that he requires surgery soon for a lung condition.

Mr Scoffield says that none of the the issues raised by Ofgem were acted on and "subsequently turned out to be difficulties with the scheme".

"Do you still feel DETI did maximise Ofgem's input from the lessons they had learned?" he asks.

Ms Hepper replies that "in the context of the time, yes we did" and that DETI did not lose sight of some of the issues.

Image source, RHI Inquiry

The legal firm Arthur Cox was commissioned to produce a final draft of the scheme's regulations, but Mr Scoffield wants to know why it was asked to do that before the scheme had been approved by DETI's casework committee.

Ms Hepper says that was "in the context of the resourcing that we had, the timeframe that we were working to" - basically, the department wanted to "keep work on track".

In her written witness statement, external, Ms Hepper says there was a need for "regular review" of the RHI scheme due to "the concern in relation to gaming".

But Mr Scoffield puts it to her that it would've been better "at the very start, to minimise the opportunity for gaming" rather than "wait and see what emerges" when the scheme was running.

The former DETI energy boss says that because the scheme was new and untested it was decided to do both - do the best it could in the regulations to prevent gaming while also keeping a eye on what happened "on the ground".

"That's the approach DECC would've taken as well," she adds, echoing her earlier point that her department followed in the footsteps of what was done in the GB RHI scheme.

Ms Hepper says it was DETI's intention that only useful heat would be deemed eligible under the scheme.

Mr Scoffield puts it to her that Ofgem was advising DETI that it was critical that that matter was addressed in the draft regulations.

Image source, RHI Inquiry

He asks her if the matter should not have been dealt with at the very start.

Ms Hepper says that at that stage DETI's view was that "the regulations and the guidance would have been sufficient that only useful heat would have been incentivised".

She says DETI's decision to address the gaming of issue in the guidance mirrored the approach taken by the Department of Energy and Climate Change (DECC) in what it did in its Great Britain RHI scheme.

This morning the inquiry is looking at the creation of the regulations for the RHI scheme.

The scheme's administrator Ofgem has already told the inquiry that it raised several red flags to DETI about problems with the regulations and advised the department about how to tighten them.

One of the issues was on the so-called gaming of the scheme - that is the installation of multiple small boilers instead of one large, more efficient boilers in order to collect a higher tariff on offer.

Image source, Getty Images

Ofgem said DETI should add a "defined term" in the regulations "to ensure clarity" on the issue of gaming, and it was "not acceptable" for the issue to be addressed just in the accompanying guidance.

Ms Hepper accepts that gaming became a major problem with the scheme but she says DETI and Ofgem ultimately agreed that covering it in the guidance was sufficient, in spite of what the administrators had said before.

Inquiry chair Sir Patrick Coghlin points out that there is no written record of the decision to "reject" Ofgem's original advice and asks why there is no recorded rationale behind the decision.

"If find it difficult to understand, from a public point of why, why there wasn't a system for recording quite significant issues such as this," he adds.