Mr Wightman circulated key details about proposed changes to the RHI scheme with the poultry and renewable industries in the summer of 2015.

The changes - which were designed to control the cost of the initiative as the number of applications increased - were made in November that year.

Image source, PA

In his witness statement, Mr Wightman says he consulted with industry "to inform the policy proposals and my subsequent advice to the minister" given that civil service guidance is that all policies should be based on evidence.

In its evidence to the inquiry, the Department for the Economy - formerly DETI - acknowledges that point but suggests Mr Wightman's consultation should, as Mr Aiken puts it, have been "less naively conducted".

There's a brief discussion of the merits of electronic documentation systems and the old days of hard copy.

Mr Wightman suggests that there may have been a temptation in the past for civil servants to print stuff and later shred it.

Image source, RHI Inquiry

Sir Patrick says that "no doubt the legal world will be very interested in hearing Mr Aiken say that electronic libraries are not the answer!"

"I surround myself with papers, as you know, Mr chairman," Mr Aiken replies, sweeping his arms across the many lever arch files he likes to spread across the desk.

The team working on the RHI scheme when it ran badly out of control should have taken "time out to actually understand" the initiative, admits Mr Wightman.

The three key civil servants who were running it from the scheme's conception in 2011 all left the department within a few months of each other in 2013 and 2014, leaving a completely new team to deal with it.

Image source, Getty Images

Mr Wightman says that give their workload when they came into the roles it was "very difficult to make that sort of time" to properly understand the scheme.

He says there were things he later found out that made his "stomach just [drop] further and further and further" in a "sense of panic".

"If those things had been known sooner... we might've been able to avoid that."

Inquiry panellist Dr Keith MacLean asks the witness if he's the type of person who, when given important documents, "will not rest until you've read it all", or if he's someone who's "happy just to know there's a document" somewhere to which he can refer if need be.

"I would like to say I'm the first person but I'd be perfectly honest and say I'm probably the second," says Mr Wightman, adding that his workload makes it "difficult to get through all the documents".

Image source, Getty Images

Documents regarding the RHI scheme were often "very long and very technical" and even when "going through it at a slow pace I still struggle with some of the content".

He tends to "scan" papers but he acknowledges that there's a risk that important points can then be missed, especially when it's something he didn't have an expertise in.

Sir Patrick tries to extract from Mr Aiken a clear steer on how many version of the handover document there were and who held them.

"There are many more than three," says the inquiry counsel, adding: "There is a clean version and then a series of different, annotated versions over time."

DETI itself never possessed the original version.

Image source, RHI Inquiry

"Nobody it seems utilised this document in the way that it ought to be utilised, which is that it would be placed within the internal DETI system," Mr Aiken says.

Mr Wightman interjects to say that putting it into the civil service record-keeping system "is one thing, but if you don't know it's [there] it's very difficult to find".

"I couldn't have made the point better myself, Mr Wightman" says Sir Patrick.

Mr Wightman makes it clear in his latest witness statement that he wasn't trying to mislead or withhold information from the inquiry when he only provided it with three pages of the 14-pages handover document.

The period of the career in which he was running the RHI scheme was "particularly mad and it was just really busy and a lot that is a blur", he tells the inquiry.

In his latest witness statement regarding the RHI scheme handover issue, Mr Wightman says he doesn't accept that a handover alone "is the appropriate vehicle for ensuring critical issues are escalated and taken forward".

He claims that "important issues... should have been made clear to senior management" by being recorded in broader documents detailing departmental priorities.

Image source, Getty Images

He agrees when Mr Aiken puts it to him that the handover notes wasn't "how information transfer for this scheme should've taken place".

"I would've expected - wrongly now - [for] a lot of those issues to be captured in other documents," Says Mr Wightman.

Mr Aiken puts two possible scenarios to Mr Wightman about how he handled the RHI scheme handover note.

"Either you did read it all and don't remember doing that and the significance of the contents beyond the first three pages did not get translated by you into action," says the inquiry barrister.

Image source, RHI Inquiry

"Or the alternative is that despite having had it you just didn't read it."

Mr Wightman says the first of those "is probably the more likely one" but he can't remember either way.

Mr Wightman maintains that he can only remember seeing three pages of the RHI scheme handover note.

Inquiry chair Sir Patrick Coghlin questions why he didn't read the whole paper, given that it outlined key information about the initiative he was about to take responsibility for in June 2014.

Image source, RHI Inquiry

"You know what a handover document is for - to provide continuity," adds Sir Patrick.

"I agree with you, chair - I should have read it," admits Mr Wightman.

Mr Aiken notes that Davina McCay, who worked on the RHI scheme just before Mr Wightman took up his role, did not save her annotated handover into the civil service document recording-keeping system.

Mr Wightman was therefore the only the person who had the full copy of this version of the note and was able to lay a hand on it in September 2016 - he agrees that it "certainly looks like" he was the only person with the annotated note.

Image source, RHI Inquiry

"You must have had it," says inquiry chair Sir Patrick Coghlin (below).

Mr Wightman agrees, saying: "The problem is I just cannot remember and it's difficult to confirm when you can't remember things.

Asked by Sir Patrick why he submitted just three pages of it to the inquiry, the witness says: "I was genuinely writing my statement to the best of my knowledge at the time and I thought: 'This is all I remember discussing.'"

Mr Wightman has told the inquiry that he found the full 14-pages handover document regarding the RHI scheme in September 2016, just as Stormont's Public Accounts Committee (PAC) was beginning its investigation into the debacle.

The reason he gave for only providing three pages of it to the inquiry was that was all he could remember receiving when he joined DETI two years earlier.

Asked if about his reaction when he discovered there was much more to the paper than he'd originally thought, he says he was "shocked and surprised".

"I certainly was surprised and quite worried that I hadn't picked up on these 11 pages."

Asked if he informed anyone more senior in the department about it - including the permanent secretary Dr Andrew McCormick (above) - in briefing them for their appearances before the PAC, Mr Wightman can't remember doing so.

Back in March, much of the questioning Mr Wightman faced related to a handover document he received when he joined the enegy team in DETI.

The note outlined some key issues with the RHI scheme that his predecessor felt needed to be dealt with urgently, including a review of the subsidies on offer through the scheme.

Image source, Getty Images

Mr Wightman originally told the inquiry that he only received three pages of the 14-pages handover and he included them as part of his evidence submission.

But it emerged that he'd received the full document, he didn't read them all - he later told the inquiry that he "wasn't trying to hide anything" when he only supplied three of the 14 pages of it in his evidence submisson.

That's the first issue on today's agenda and Mr Wightman has provided a new witness statement that deals with the matter, external.

Having already appeared before the inquiry in March, Mr Wightman is already sworn in so we're straight into the questioning.

He's given a further witness statement , externalin the light of answers he provided during his previous visit to the Senate chamber.

Image source, RHI Inquiry

To recap, Mr Wightman headed DETI's energy efficiency branch from June 2014.

That meant he had oversight of the non-domestic RHI scheme and also worked on developing and introducing the domestic RHI scheme.

The inquiry's junior counsel Joseph Aiken is asking the questions today.

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.

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 late-2016... and the fallout from the scandal attached to it is still being felt in the region's politics today.

Image source, Getty Images

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.

It's a beautiful, sunny morning here at Stormont... but we've decided we'd rather be sitting indoors reporting on the Renewable Heat Incentive (RHI) Inquiry.

Today's witness is Stuart Wightman, who was head of energy branch at Stormont's Department of Enterprise Trade and Investment (DETI) that was running the RHI scheme from June 2014.

Image source, Reuters

Mr Wightman last appeared before the inquiry in March.

Why not stay with us for what should be an interesting day?