In Mr Bell's (below) evidence to the inquiry, he alleges that communications between himself as DETI minister and the department were "overseen and filtered" by his special adviser Timothy Cairns.

Mr Cairns "filleted information" about the RHI scheme, according to Mr Bell, and was "in a position to, and did, exercise considerable control in respect of the agenda of the weekly ministerial issues meetings".

Image source, Press Eye

Mr Scoffield says the "picture painted" by the former DUP MLA is that he believed he was being "manipulated" and "kept in the dark" about what was happening in his department.

When Mr Bell first made the claims to the BBC last year, Mr Cairns publicly denied them.

A "great deal of the controversy" in the RHI scandal arose from former enterprise minister Jonathan Bell's interview with the BBC's Stephen Nolan in December last year, says Mr Scoffield.

He had replaced Mrs Foster as DETI minister when she moved to the finance department in May 2015.

In December, Mr Bell - then no longer the minister - had gone back to the department to view documents relating the scheme, accompanied by the then permanent secretary Dr Andrew McCormick (above).

He made recordings of the conversations and recounted them in the BBC interview.

Mr Scoffield says those recordings have been submitted to the inquiry and Dr McCormick has also received them and has since given evidence to contextualise them.

DETI's energy division had a serious problem when it was ordered by the department's finance branch to stop spending in May 2015.

In his evidence to the inquiry, John Mills, the head of the energy division at the time, says there was "no off switch in the RHI scheme".

Image source, Getty Images

Mr Scoffield says a "highly important consideration" for the inquiry will have to "determine what gear" the initiative should have been in from that point on - "hard in reverse"; "full scale ahead" due to its success; or in "neutral - we cant close it but let's not try to make matters any worse".

He says there was a "subplot" of "tensions" between DETI's energy and finance divisions at this stage.

Mr Scoffield notes that the RHI scheme's budget issues that were raised in March were not drawn to the attention of the then DETI minister Arlene Foster.

The "big concern" in March 2015 was the budget of the RHI scheme says Mr Scoffield and the increased applications meant the initiative was going to spend more money than had been allocated to it.

Two months later it was clear that unless more money was made available by the Treasury, or DETI was allowed to carry forward money not spent in the scheme's early years, spending in 2015 was going to go beyond its budget was.

"That was the warning - that was the alarm bell," says Mr Scoffield.

Mr Scoffield says there were competing views within different DETI divisions about how to deal with this.

He says that staff in the energy division said: "This is a great success - we should argue for more money."

But its finance division responded bluntly: "Stop spending, we can't afford it. Don't go over budget."

DETI "lost sight of the requirement" to seek approval in March 2015 for the continued running of the RHI scheme, says Mr Scoffield.

Department of Finance and Personnel (DFP) support for the scheme expired that month and the failure to have secured it was another "missed opportunity" to assess the scheme.

Image source, DFPNI

DFP granted approval later in 2015 for an amended version of the scheme, but it refused to give retrospective approval from March 2015.

In its evidence to the inquiry, the Department for the Economy - formerly DETI - says it regrets missing that approval point in March 2015 because that could have been a point at which crucial cost controls could have been added.

Throughout 2014, the RHI scheme was taking off, Mr Scoffield says, with a trend emerging of ever greater numbers of applications in each of the year's quarters.

Boiler installers were promoting the scheme's benefits, and the inquiry hears that one firm's director jokingly said that RHI stood for "real hectic industry".

Image source, Getty Images

Estimates in 2014 suggested that in March 2015 there was expected to be about 300 applications but when that date came around there was almost double that number.

DETI said that there were no longer any concerns about low uptake of the scheme, which had been expressed in its early stages... and it was at this point that "the penny dropped that the scheme was going over budget", says Mr Scoffield.

Mr Hutchinson's note of August 2014 lists immediate actions to be taken by the end of the year.

Mr Scoffield refers to one particular page, which he says is "potentially very significant".

Image source, RHI Inquiry

There are seven key bullet points, one of which calls for a review of the RHI scheme.

"The two-sub-points are that a review of biomass tariffs under 100kW was required, and that consideration should be given to tiered tariffs to prevent excessive profits," Mr Scoffield says.

Matters move to a handover note about the RHI scheme from DETI official Peter Hutchinson, which Mr Scoffield says came at a "watershed moment" for the initiative in mid-2014.

He and others in DETI were moving to new posts elsewhere, and left the note for successors who would take on their responsibilities at the department.

Image source, Getty Images

It was being prepared just as a "confluence of alarm bells" were going off about the initiative, he adds.

The note warned that an "urgent review was required" because "signs of concerns had begun to appear", Mr Scoffield says.

Mr Scoffield turns to the publicising of the scheme, and a number of promotional events run, or attended by, the renewable heat industry while the scheme was operational.

He says that the benefits of the scheme were presented and marketed "and at least several of these look as if they may well have been attended by public servants".

Mr Scoffield then gives an example an event held by Action Renewables, a body that supports renewable energy development, in June 2013.

He displays a leaflet promoting the event, which bears the words: "Book now to find out how to generate heat and get paid for it - the Renewable Heat Incentive explained".

The project team behind the Desertcreat college told the then justice minister David Ford (below) that Sheridan & Hood's proposal was "flawed" and the intent behind it appeared to be a "rather cynical attempt" to capitalise on the scheme.

It seemed to them, Mr Scoffield says, that it was "too good to be true" and the Department of Justice declined the proposal.

Image source, Press Eye

But it did not refer the letter with the building firm to DETI, and therefore whether it handled that correspondence properly is a matter for the inquiry to consider, says Mr Scoffield.

It was not the only Stormont department to be made aware of the benefits of the scheme - the then finance minister Sammy Wilson was contacted in December 2012 by another firm that outlined the remarkable advantages on offer.

Sheridan & Hood began marketing the RHI scheme's benefits to potential customers, one of which was Stormont's Department of Justice.

As the department was developing its plan for a new police, prison and fire officers training college at Desercreat in County Tyrone (below), the building firm was asked to provide costs for the site's energy system.

Image source, DoJ

The company wrote to the then justice minister David Ford less than a month after the RHI scheme started, putting forward a proposal that the department could turn the system's running costs into a "profit".

Sheridan & Hood suggested that small 99kW boilers eligible under the RHI scheme could be used for the college's heat system and it said the department could collect £894,800 over the initiative's 20-year term.

The firm was "making absolutely no bones about" the RHI scheme's overgenerosity, says Mr Scoffield.

Evidence the inquiry has seen suggests that Ms O'Hagan's warnings to DETI about how the RHI scheme was being capitalised on by some claimants was "far from the only" instance in which civil servants arguably should have noticed that it was "too good to be true", says Mr Scoffield.

He outlines what he describes as "red-flag moments", including that it was a "open secret" in the energy industry that the scheme was overgenerous.

One boiler installation firm - Sheridan & Hood - "very quickly realised the benefits of the scheme".

Its director Brian Hood has told the inquiry that it was awarded a certificate from Mrs Foster for being the first company to become accredited on the scheme.

Further contact between Ms O'Hagan and DETI officials is outlined by Mr Scoffield, and he describes her as "persistent voice of warning in the department's ear" for almost two years.

He says she was "incentivised" to raise her concerns because of the adverse affects of the RHI scheme on her business.

But what she was complaining about "was, or at least, may have been correct" and deserved "greater investigation".

An early assessment of this part of the scandal, Mr Scoffield says, is that DETI's failure to act on her concerns was a "highly significant missed opportunity" to identify the critical errors in the RHI scheme.

Ms O'Hagan told the DETI officials that she could provide proof of her claims that those using the RHI scheme were effectively burning fuel to earn money.

From her point of view, her warnings had been ignored, and Mr Scoffield says it's "easy to see" that it appeared that nothing was being done.

Image source, RHI Inquiry

But he adds that the "lack of credulity" about her claims on the part of the DETI officials may have been down to "naivety rather than anything more sinister".

One of the officials - Peter Hutchinson - did, however, note Ms O'Hagan's concerns, saying in a handover note to new civil servants at the department that they needed to be looked at further down the line.

In her evidence about her meeting with DETI officials, Ms O'Hagan says they discussed her business and her concerns about the overgenerous tariffs available on the RHI scheme.

Ms Hagan says she told the officials what she was seeing on the ground was that buildings were using "way more energy than before" because the operators were being paid to do so.

Image source, RHI Inquiry

Mr Scoffield explains that Ms O'Hagan says the DETI officials did not agree that was the case because "they didn't believe people would do that".

He says that is not the view shared by Fiona Hepper, the director of DETI's renewable energy team, in her evidence, whose view is that Ms O'Hagan's views were not dismissed, but simply that the department asked for evidence to support them.

An earlier email that Ms O'Hagan had sent to DETI, in which she requested a meeting with the minister, had been replied to by Mrs Foster, who instead offered a meeting with her officials.

Mr Scoffield says that Ms O'Hagan met the officials in October 2013 but her concerns "were not escalated to ministerial level".

On the evidence, he adds, that appears to be the case but it "could be to miss the point" because the concerns had been "communicated directly" to Mrs Foster "in the first place".

In an email on 3 September 2013, Ms O'Hagan sent an email to Arlene Foster to say that the RHI scheme "pays claimants to use as much heat as they can", so that the incentive to use more is "leading to misuse in some cases".

Image source, Reuters

Mr Scoffield says this email is "potentially significant" because it is a "clear message" delivered "directly" to what the then enterprise minister has told the inquiry in written evidence is her "personal email account".

Evidence from DETI is that checks of email records show "no trace" of the email being forwarded on to its officials - in fact, it was first seen by DETI in March 2017, after the inquiry had been set up.

The case of the so-called "whistleblower" who contacted the then enterprise minister Arlene Foster to discuss the operation of the RHI scheme in August 2013 is raised by Mr Scoffield.

She is Janette O'Hagan, who runs a company selling technology that helps to make businesses more heat efficient.

As the inquiry heard on Tuesday, she had requested anonymity but had that refused by inquiry chair Sir Patrick Coghlin.

Mr Scoffield says it became clear to her that a number of companies in the RHI scheme "did not appear to be interested in trying to save heat" - that, of course, was against the intention of the initiative.

He explains that the the Department of Enterprise, Trade and Investment (DETI) refers to her as a "concerned citizen" rather than a "whistleblower", and Ms O'Hagan does not consider herself to be a whistleblower.

Mr Scoffield picks up from where he left off yesterday, talking about greatest threat that existed to the scheme - the biomass tariff for small to medium-sized boilers was higher than the cost of fuel.

He describes this as the "perverse incentive"to burn fuel to earn money.

Image source, RHI Inquiry

Mr Scoffield says that, in its statement to the inquiry, the then Department of Finance and Personnel (DFP) maintains that the main design flaw in the scheme "was not recognised, or understood by officials throughout the whole period of operation of the scheme".

According to DFP, that did not become clear until the Northern Ireland Audit Office's report on the scheme, external in June 2016.

Proceedings open with a warning from inquiry chair Sir Patrick Coghlin, who says witnesses should not be "put under pressure" by the media.

He says he does not expect witnesses mentioned in the inquiry's opening statement to be questioned by the media before he has heard their account.

"The inquiry is to have control of the evidence, not the media," says Sir Patrick.