Despite his best efforts, Mr Lunny has run out of road - it's knocking-off time and he still has a good hour's worth of questions to get through.

Image source, AFP

Sir Patrick must be in a forgiving mood as he agrees to an extra session on Friday afternoon to bring Mr Thomson's evidence to an end.

The much-feared snowstorm - the so-called Beast from the East - has yet to hit Stormont, so we'll be back at 09:45 tomorrow if it spares us... join us then.

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Former DETI minister Arlene Foster and senior civil servants knew the department delivering the RHI scheme was "badly under resourced" but still decided to go ahead with the project, the inquiry heard.

Image source, Press Eye

David Thomson, a retired former senior manager at the department, said there was a staff shortage in a "critical area".

He also said the initiative "wasn't ignored" by DETI's top management team but bosses and the minister decided not to make it a priority.

A review of the RHI scheme was to take place in 2014, and the project had originally been signed off on the guarantee that that would happen.

But it never did, and a key chance to spot some of the major flaws in the initiative was missed.

Image source, Getty Images

DETI's operating plan for the 2013-14 year makes no mention of the review, and Mr Thomson acknowledges that it should've been in that document.

It's also missing from the 2014-15 plan, with Mr Lunny describing those omissions as "important" and which "ought not to have occurred".

Mr Thomson says he assessed in 2012 that the take-up of the RHI scheme "may not be huge" because, generally speaking, businesses weren't investing and banks weren't lending money.

That was one consideration as to why DETI decided not to introduce cost controls in the initiative that were being added to the similar scheme in Great Britain, he explains.

Image source, Getty Images

The scheme's administrator, Ofgem, had warned DETI in June 2012 to hold off on the project until it had added the budget protection measures.

DETI had two options: add the cost controls immediately but that would delay the opening of the scheme; or open the scheme first and add the controls later.

Mrs Foster endorsed the second of those, and Mr Thomson says he believed the cost controls would be added within a year or 18 months of that.

In March 2012, the RHI scheme was considered by DETI's casework committee, an internal scrutiny panel that had to approve projects before they went ahead.

That process was intended to be a thorough consideration of scheme's strengths and weaknesses, but Mr Lunny questions its effectiveness.

The presentation was made by Ms Hepper, a grade five DETI official to three of her fellow grade five officials.

Most of them, Mr Lunny observes, worked along the same corridor at Netherleigh, DETI's headquarters just down the road from Stormont's Parliament Buildings.

He describes it as "a peer review, but a peer review by people that you may be in very regular contact with on a daily basis"... so did that impede its effectiveness?

"No," says Mr Thomson, "It is a very robust process".

Inquiry panellist Dr MacLean asks whether, when the £111m projected cost increase in the RHI scheme took the project "to the brink of stopping it", the minister should have been informed of what had happened.

Mr Thomson says he can't remember to what extent Mrs Foster was told about the rise.

Image source, RHI Inquiry

Mr Lunny points out that there are no records of the discussions on the issue that Mr Thomson claims he had with the team working on the RHI scheme and Ms Foster.

The witness says he "can't believe" he wouldn't have raised it with the minister.

The projected spend on subsidies in the RHI scheme increased by £111m to £445m in a further report produced by CEPA in February 2012, external.

The big rise was the result of changes to the subsidy rate on offer that were required on the basis of new evidence that DETI had found.

Mr Thomson says he "scanned" CEPA's report and "would have spotted things like those changes".

Image source, CEPA

Asked if the increase caused him any concerns about the scheme's value-for-money, he says "it raised the question of: 'Do we stop?'" but he can't remember why DETI decided not to stop, though.

Mr Lunny points out that the subsidy cost rise was almost 33%, and asks how much the increase would have to have been for the department to decide to send the project "back to the drawing board".

Again, he can't remember his thinking at the time but he says he was happy for the department to proceed in site of the extra £111m spend.

DETI's energy team sent a submission the the then minister Arlene Foster in June 2011 outlining the options and recommendations for the RHI scheme, as drawn up by external consultants.

In the submission, it was claimed that an ongoing subsidy scheme was the "preferred approach" and offered the "highest potential renewable heat output at the best value".

Image source, Getty Images

But the analysis that the consultants had carried out found that an up-front grant fund was actually a better option in that regard, and Mr Lunny describes the content of the submission as "potentially misleading".

Mr Thomson, who earlier said he would've seen all submissions made to the minister, tells the inquiry that there was no intention in that paper on the part of civil servants to "give the minister a firm recommendation as to which one to go for".

"I do recall we were keeping the two options open," he says, adding that if the mistake had been spotted he wouldn't have expected it to be repeated.

Picking up after lunch, Mr Lunny turns to the period in 2011 when the choice was to be made between an up-front grants-based initiative - known as a challenge fund - and the ongoing subsidy scheme that became the RHI.

Consultants at Cambridge Economic Policy Associates (CEPA) had estimated the cost of a subsidy scheme would be £334m, and put a grants fund at £161m, and they said the grants model would have delivered more renewable heat.

Image source, RHI Inquiry

Would Mr Thomson have been bearing in mind value for money when endorsing the choice of an ongoing subsidy scheme over a grants fund?

He says value for money "was a difficult assessment" for the RHI scheme.

The witness refers to the Aecom Pöyry research paper of 2010 that was produced for DETI, which he says advised against short-term projects in delivering renewable heat.

He says he didn't read all of the CEPA report: "I did read the conclusions and recommendations."

It was becoming more common for civil servants not to take notes of key meetings with the DETI minister during Mr Thomson's time at the department, he says.

"It happened maybe more than it should have, but then maybe I'm old-school - I was in the habit of doing file notes of a meeting and recording it," he adds.

Image source, Getty Images

He says those notes would've included what the minister decided or instructed, adding: "Someting like that there should be a record of, I think."

But he tells the inquiry a "greater informality" was creeping in with other staff, which Sir Patrick says was "asking for trouble".

With that, the inquiry rises for the lunchtime break.

The RHI scheme was to be paid for under a form of demand-led funding called annually managed expenditure, external (AME), which is normally open-ended and paid for by the Treasury.

But in the case of RHI there was a novel form of "capped" AME.

Mr Thomson says that he understood that if the scheme went over budget DETI "would have to fund that ourselves".

Image source, Getty Images

Sir Patrick wants to know what steps Mr Thomson took to ensure that officials knew that this was "a totally novel form of funding".

"We had discussions in the department and gave advice to the minister," he replies.

"What about telling the people who were going to operate the scheme?" Sir Patrick asks, with mr Thomson saying he's sure he would have spoken to Ms Hepper about it.

It "doesn't appear" that the RHI scheme was "formally or perhaps properly project-managed", according to Mr Lunny, who asks whose responsibility it was to ensure that did happen.

"I'm not sure I would want to put any one person on that - this is a corporate failing," replies Mr Thomson.

Image source, RHI Inquiry

He says Ms Hepper was responsible for the management within the energy branch, but adds that he was her line manager.

"You would expect that if one person drops the balls there is a check and a balance to pick it up."

"All was peaceful and calm" about the RHI scheme inside the civil service while "the outside world was fully aware" of the enormous benefits that were on offers, says Sir Patrick, who wants to know why that was the case.

"I don't know," says Mr Thomson.

Image source, RHI Inquiry

"The reason the inquiry's here is because something fundamentally went wrong that none of us who were there at the time suspected," he adds, saying he never thought he'd be sitting at Stormont answering questions about it four years after his retirement.

"If it's any comfort to you, I never thought I'd be sitting in an inquiry after I was retired either," laughs the chair.

As we've heard in previous witness sessions, a risk register was created for the RHI scheme in March 2012, but it was never updated or amended to reflect changes in the project.

Mr Lunny gives an example - the external consultants who drew up the basis for the scheme warned DETI that it would never be able to single-handedly achieve a target of producing 10% of Northern Ireland's heat from renewable sources by 2020.

Image source, Getty Images

That should have appeared in the risk register.

Mr Thomson says he doesn't recall being made aware of that warning, and adds: "Looking back at this, project management was clearly a weakness."

Sir Patrick suggests the decision not to form a monitoring board for the RHI scheme was one of "such significance" that Mr Thomson should've recorded it.

"I have difficulty in seeing how it could be signed away in an informal conversation," he adds.

Image source, Getty Images

Mr Thomson says he understood that the regular contact between DETI and Ofgem was "effectively a project board", even though it wasn't what the administrator had recommend.

Mr Lunny points out that the scheme was of such complexity, but Mr Thomson stands by his view that "at the time" he believed the less formal arrangement was sufficient.

One suggestion that was put forward to help manage the RHI scheme and mitigate against the risks that were associated with it was a monitoring board.

It was to be made up of DETI civil servants and staff from the scheme's administrator Ofgem, who would scrutinise the initiative's operation and costs and make any changes that would be needed.

Documents proposing the board suggested that would be better than "taking a reactive approach should scheme costs grow beyond the proposed budget".

Image source, Getty Images

The project was signed off by an internal DETI scrutiny panel on the basis that the board would be established.

But it was never set up and Mr Hutchinson has told the inquiry that it would've been useful.

Mr Thomson says he later found out that the board didn't exist and claims he was assured by DETI's energy boss Ms Hepper that civil servants were in "regular contact" with Ofgem, which fulfilled the same purpose.

Mr Lunny's introduction of project management includes a process called gateway review.

The Department of Finance website describes that as "a series of independent peer reviews at key stages of a programme or project lifecycle, aimed at ensuring its successful delivery".

Image source, RHI Inquiry

He raises an email exchange in which Ms McCutcheon asked Ms Hepper (above) whether the RHI scheme should be gateway reviewed.

Ms Hepper replied: "I don't think we need gateway for RHI - we have the project finished and moving into implementation so probably too late in any case."

After the mid-morning break, Mr Lunny turns to the lack of project management in the RHI scheme.

Mr Thomson confirms that he was involved in a number of formal projects, including Titanic Belfast, as we heard earlier, and a poultry litter scheme.

Image source, RHI Inquiry

Mr Lunny quotes from the Northern Ireland Guide to Expenditure Appraisal and Evaluation, external (NIGEAE), which lays down the need for project management in government programmes.

It says "effective management of projects is an essential element of resource control" to ensure projects are managed effectively and within budget.

Ms McCutcheon, who headed DETI's the renewable heat branch between 2011 and 2014, has said that Mr Thomson only spoke to her once in those three years.

Mr Thomson says he's "not going to challenge what she said".

Image source, Getty Images

Dr MacLean says he finds that "there's a big gap" between that view and Mr Thomson's insistence that he regularly walked across to the department's energy division "fairly regularly".

"Maybe it wasn't as frequently as I thought I did," replies the witness.

Inquiry panel member Dr Keith MacLean wants to know if the problem of under-resourcing in DETI's renewable energy branch was raised with senior management.

"There no alarm bells ringing to me; there were no red flags," says Mr Thompson.

He adds that if people had come to him saying there was an absolute crisis in resourcing "that might have triggered me to say this is something I need to get personally involved in".

Image source, Getty Images

He says it was his understanding that resources were adequate to meet the objectives in the department.

Dr MacLean asks him if he was aware that there were 77 officials working on the GB RHI scheme in Whitehall.

"I knew they had a team of 77, but that's very common," he replies, explaining that running departments under devolution is a "very difficult thing to manage" because Stormont departments have to replicate their Whitehall counterparts but with much smaller resources.