Image source, AFP

Plenty more questions for Mr Cooper still to be asked, it seems, but that will have to wait.

The inquiry is off for a couple of weeks but never fear, it will return - we'll be back on Tuesday 10 April.

Have a wonderful Easter!

BBC News Northern Ireland

A senior civil servant has accepted that there is "no evidence" to back his claim that Arlene Foster decided to drop cost controls from the RHI scheme.

Image source, Press Eye

John Mills, a former energy boss at DETI, made the claim in October 2015 as major changes were being made to the subsidies on offer through the scheme.

But he told the inquiry that he had made an assumption that the then DETI minister had given her authority for the move and his view had been "completely incorrect".

Inquiry chair Sir Patrick Coghlin is deeply unimpressed by the level of detail in the minutes of the DETI casework committee meeting, at which the RHI scheme was approved.

He notes that key matters that Mr Cooper claims were discussed are not fleshed out as much as he would like to see.

Image source, RHI Inquiry

The witness, who signed off on the minutes, tells the chairman that some of the key issues are mentioned "implicitly".

In a withering tone, Sir Patrick responds: "I should've thought from a common-sense point of view that an implicit minute is not a particularly helpful document."

There was no way that DETI could've got its hands on the extra £3.5m for admin costs to run the much cheaper model of the RHI scheme.

The challenge fund was going to cost £5m whereas the subsidy model - which was ultimately chosen - could've been managed for £1.5m, even though its overall cost over 20 years would top £300m more than the alternative.

Image source, Getty Images

Mr Cooper says that neither Stormont's finance department or the Treasury would've handed over the extra money to run the cheaper scheme.

That was a big factor, he says, and meant that the only viable option for the RHI scheme was the vastly more expensive subsidy model.

Image source, Getty Images

Mr Cooper says he raised concerns at DETI's casework committee meeting that the RHI scheme would see a lot of money spent for very little benefit in terms of increasing renewable heat production.

But that intervention isn't mentioned in the meeting's minutes.

He was eventually persuaded to approve the scheme, in part because Northern Ireland would have faced substantial fines from the EU if targets for green heat production by 2020 had not been met.

A key question for the inquiry to find an answer to is why DETI chose to turn down a model for the RHI scheme that would've ended up hundreds of millions of pounds cheaper.

There were two options on the table at the outset: an up-front grants model and an ongoing subsidy offer that would run for over 20 years.

The grants scheme, known as the challenge fund, was rejected because the initial administrative costs were £5m while the subsidy scheme cost £1.5m.

Image source, Getty Images

The subsidy scheme was chosen, even though its total costs were £300m higher than the alternative.

Mr Cooper says he believed the grants model was a "much bigger risk" than the challenge fund because it had to be designed from scratch.

His view at the time was that the proposed ongoing subsidy initiative would've been a fairly simple copy of the Great Britain RHI scheme, which was already up and running at the time.

Increasing the production of heat through renewable sources was a "national priority", says Mr Cooper, so much so that the UK government was willing to spend hundreds of millions of pounds to achieve that.

That commitment "was reinforcing" to him and his colleagues on the DETI scrutiny panel that was considering the RHI scheme for approval that the programme was "really important".

Image source, Getty Images

Mr Aiken questions whether that view meant that there was less scrutiny applied to it by the panel.

Not the case, argues, Mr Cooper, who says the panel's meeting to discuss the project was "one of the longest... that I've ever been in, to be frank".

"We took that responsibility seriously."

On to the questions now and the afternoon's witness is Trevor Cooper.

He was a finance director at DETI during much of the time when the RHI scheme was running and had an important role in approving it when he was the chair of the departmental panel that scrutinised it.

Image source, RHI Inquiry

He's been here before, back at the start of February, when he said then that he approved the scheme on the understanding that it had a "big red button" that would allow it to be stopped if too many people applied to it.

Mr Cooper's written statement can be found on the inquiry's website, external.

Picking up after lunch is the inquiry junior counsel Joseph Aiken and he has an update for the panel regarding evidence given by civil servant Stuart Wightman (below) on Wednesday.

The former DETI civil servant - who worked directly on the RHI scheme from summer 2014 - was questioned about why he only included part of a key document in his evidence submission to the inquiry when he in fact had possession of the whole thing.

It was a handover note from the time he joined the department and it outlined some of the big issues with the scheme that needed to be addressed.

Image source, RHI Inquiry

He told the inquiry this week he hadn't been trying to hide anything, and Mr Aiken says that version of events is indeed fair.

The inquiry has since had a dig and found that Mr Wightman declared in March last year that he had possession of the full document and he offered to submit it.

Mr Aiken says the inquiry "takes our obligation of fairness very seriously", hence the importance of pointing out Mr Wightman's submission at the earliest opportunity.

Mr Mills is done for the day, but there are still many questions to be put to him some time after Easter.

The inquiry's taking a break for lunch, but we'll be back at about 14:00 for the afternoon session.

Mr Mills told an internal DETI panel in 2015 that the decision to push ahead with opening the domestic RHI scheme instead of adding cost controls to the non-domestic initiative had been taken by the minister, Mrs Foster.

He now accepts that that was "completely incorrect".

Image source, Getty Images

He says his answer at the time was based on an assumption that there had been "ministerial authority" behind the decision.

But in looking through the documents since then, he's found "no evidence" to back up his original claim.

The Northern Ireland Civil Service "does not have the expertise" to run its own complex programmes such as the RHI scheme, Mr Mills tells the inquiry.

He says that Northern Ireland needs to be part of UK-wide schemes run from Whitehall.

Image source, AFP

"If I could change one thing about the RHI it would be not to do a separate Northern Ireland scheme," he says.

"I wouldn't want to leave you with the impression I didn't challenge but I didn't challenge the RHI direction of travel, unfortunately."

The addition of cost controls had been included in a public consultation DETI held in the second half of 2013 about the development of the RHI scheme that would happen the next year.

Inquiry panellist Dame Una O'Brien asks whose responsibility it was that they never materialised.

Mr Mills says it should be "shared" between a number of people.

But he accepts that he didn't "know enough to have questioned the... course that was already set".

DETI had drawn up a plan to expand the RHI scheme in 2014 - it was to include the addition of cost controls as well as opening the initiative up to domestic users.

While the domestic scheme went ahead, the introduction of budget protection measures fell away and were not put in place.

Mr Mills says that the shortage of staff at DETI's energy team "didn't permit" both to be done at the same time, and the opening of the domestic RHI scheme was given priority.

In his written statement, Mr Mills says there was a "political saleability" issue of persuading the DETI minister Mrs Foster of the need to review and put the brakes on the RHI scheme when the emphasis was trying to increase uptake.

He explains that trying to convince her of the need to add cost controls at that time may not have been "embraced", given that uptake was low and money was being handed back to the Treasury.

Image source, RHI Inquiry

There was "quite a bit of internal political debate" about the same matter in 2015, much later in the scheme's lifetime, by which stage Jonathan Bell had taken over as the minister.

It was "obvious" at that stage that there was a need to protect the budget as the number of applications began to soar - it took three months to eventually get the crucial changes made.

When a "direction of travel" has been established", he says, "to suddenly change that is not so easy".

The RHI scheme was set up to ensure that Northern Ireland could pocket millions of pounds from the Treasury that it otherwise wouldn't have received, Mr Mills believes.

He tells the inquiry that concern over handing money back to the Treasury was more of a driving force behind trying to improve take-up for the initiative than anything else.

"Was there a general feeling within the department at that time that money going back to Westminster was a bad thing?" asks Mr Scoffield.

Image source, Getty Images

Mr Mills says that was "certainly" the case, adding that it was "money which was additional to the Northern Ireland block (grant), which could be used for supporting an important part of the economy" as well as cutting carbon emissions.

Mr Scoffield: "Does it follow there was a general feeling that trying to get as much of that money as possible into Northern Ireland was a good thing?"

"Oh, absolutely," says Mr Mills.

In May 2014, a submission - written by Mr Hutchinson and cleared by Mr Mills - was sent to the DETI minister.

It said: "It may be appropriate to review existing tariffs based on the experience of the first 18 months of the scheme."

In the same month, Mr Hutchinson wrote a handover just before he left the department, in which he said the tariffs on offer through the scheme "can be overgenerous" and that demand on the scheme was higher than expected.

Image source, Getty Images

Inquiry chair Sir Patrick Coghlin says: "Surely if ever there was an alarm bell, that was one."

But that remark didn't make it into the submission to Mrs Foster.

Mr Mills says he wouldn't have seen the handover and Mr Hutchinson "was not coming to me and saying: 'there's a crisis'".

In February 2014, an Assembly question was put to the DETI minister Arlene Foster by then Sinn Féin MLA Daithí McKay, who asked about the amount of energy generated from renewable sources.

Part of the answer, signed off by Mr Mills, said: "DETI will carry out analysis as part of a future review of the Renewable Heat Incentive."

It said it's "estimated that we're on track to achieve" a government target of having 4% of Northern Ireland's heat produced from renewable sources by 2015.

Image source, Getty Images

But Inquiry panellist Dr Keith MacLean recalls Mr Mills' evidence from yesterday, when he said the only concern at the time was that uptake on the RHI scheme was slow.

Dr MacLean questions whether the answer to the MLA's question is accurate, suggesting that there's "some confusion" over the uptake level on the scheme.

Mr Mills admits that the answer is inconsistent with the evidence he gave yesterday and he now questions how accurate it was to have told the assembly that the department was on target.

Mr Mills insists he wasn't aware of the need for a review in the first few months after he joined DETI.

But in evidence given to the inquiry, Peter Hutchinson - the DETI civil servant who worked most hands-on on the RHI scheme and who served under Mr Mills - says it was probably discussed between them at a meeting in March 2014.

Today's witness says he can't remember that: "What was being presented at that meeting was 'full-steam ahead with the domestic [RHI] scheme'," he says.

Several witnesses have said there was pressure at that time to get a new domestic RHI scheme up and running and that it was prioritised over dealing with the original initiative.

An important chance to pick up some of the fundamental defects in the RHI scheme was missed in 2014, with a review that was scheduled for then never taking place.

Mr Mills accepts that the review was a "fundamental aspect" of the scheme being approved by an internal DETI scrutiny panel and by Stormont's finance department.

Image source, Getty Images

He says there were no terms of reference for a review laid out when he began working as DETI's energy boss in January 2014.

In his witness statement, he says he "did not have the resources to fundamentally review" the initiative "or any other policy areas" and "nor was it indicated to me that a substantial overhaul review was anticipated".