It was a "universally-held" view in January 2016 that the RHI scheme needed to be closed quickly, says David Sterling.

Image source, RHI Inquiry

Asked if he sensed reluctance from anyone to the shutdown, he says he didn't - the only "debate" about it was how quickly it should be done.

"A balance had to be struck between quick closure and at the same time minimising the risk that a successful [legal] challenge might have been mounted, which could've put us in a much worse position."

After a letter from the Treasury in mid-January 2016, it became clear to everyone that the Northern Ireland Executive would have to pick up the bill for the RHI debacle and the scheme would need to be shut quickly.

David Sterling thinks the forecast for the budget overrun was about £33m.

It was fairly clear "there was no realistic prospect" that DETI could handle that total itself because the department had a total budget of about £300m, he explains.

DETI's job was to close the scheme but the tab would have to be picked up elsewhere, he adds.

There was a "vague hope" among Stormont ministers that "political pressure" would lead to the Treasury providing emergency funding to plug the big gap in the RHI scheme's finances in early-2016, says David Sterling.

But civil servants didn't see any chance of that - Mr Sterling says they advised "there wasn't any realistic prospect that the Treasury would offer more" because the government had provided extra money for Northern Ireland as part of the Fresh Start Agreement just a couple of months earlier.

Image source, PA

An internal email from the time shows that Mr Sterling believed Stormont's stock was low with the Treasury.

Asked to explain how he reached that conclusion, he says the Treasury has a general view that Northern Ireland "always does well when there are political negotiations".

Former DUP minister Jonathan Bell claimed there was a "major row" about the RHI scheme between David Sterling and Arlene Foster's adviser - Mr Sterling says that didn't happen.

Mr Bell told the inquiry he'd heard talk that the two men had been arguing, with Mr Sterling shouting at Dr Andrew Crawford: "You kept this scheme open for the benefit of your family and you've caused significant budgetary crisis in Northern Ireland."

Between them, three relatives of Dr Crawford have 11 biomass boilers registered on the RHI.

Asked about the dispute claim, Mr Sterling says that if any "sharp exchanges" had happened he "would have recalled it".

Dr Crawford told the inquiry he informed Mr Sterling he had family members who were RHI claimants in autumn 2015.

But Mr Sterling says he doesn't think Dr Crawford's family links to the scheme were "flagged up to me as a significant issue" at the time.

David Sterling says he didn't know that two DUP ministerial advisers were working together in summer 2015 on plans that civil servants had drawn up to cut the RHI scheme's subsidies.

Dr Andrew Crawford (below), who was advising the then finance minister Arlene Foster, and Tim Cairns, who was the aide to the then enterprise minister Jonathan Bell, had been instructed to work together by senior DUP adviser Timothy Johnston.

Sir Patrick Coghlin says Dr Crawford was "conducting a form of negotiation" over the subsidy cuts plan, suggesting changes that would have made it much less effective.

The inquiry chair says that's a "worrying aspect" and asks: "Where's the control that flows from the fact that [advisers] are paid public money?"

Mr Sterling pauses and says: "If a special adviser doesn't tell us what they're doing it's difficult for us to know."

In an email that summer, Dr Crawford told Mr Cairns the scheme was paying poultry farmers to heat empty sheds and there was a danger of a massive spike in applications ahead of the RHI's subsidy cuts.

DUP leader Mrs Foster told the inquiry she should've been alerted to the two issues and Mr Sterling agrees that he or the minister should've been informed.

Stormont finance officials should've "gripped" the issue of working out the funding situation for the RHI scheme in 2015, says David Sterling.

When cracks began to appear in the scheme in spring that year, civil servants at DETI sought clarity about the funding mechanism in order to help them understand how they could solve the budget problems.

Image source, Getty Images

But it took months for that to be nailed down and Mr Sterling says his staff at the finance department should've done that much sooner.

Sir Patrick Coghlin, the inquiry chair, says there was "endless correspondence" between officials at DETI and the finance department and that was an "entirely frustrating process".

Mr Sterling tells him: "I'm acknowledging that [the finance department] should've gripped it."

Jayne McCormack
BBC News NI politics reporter

In his latest witness statements to the inquiry, David Sterling says there should be a review of the role of Stormont's ministerial advisers before devolved government returns to Northern Ireland.

The inquiry has spent much time looking at the relationship between ministers and their unelected advisers, and how much power advisers had in relation to decision making.

Mr Sterling said that in response to what has emerged, he believes there is a "strong case" for a review of the role of advisers and it should be made clear to ministers that they are "fully responsible and accountable" for their aides.

The head of the Northern Ireland Civil Service since his appointment in summer last year, David Sterling has a lot on his plate, especially in the absence of ministers at Stormont.

He joined the civil service in 1978, rising up the ranks and eventually heading some Stormont departments, including the Department of Finance.

At the time of the set-up of the RHI scheme, he was the permanent secretary - the top civil servant - at the Department of Enterprise, Trade and Investment (DETI).

He gave evidence to this inquiry back in March, admitting personal responsibility for failings in the RHI scheme and saying he felt in hindsight that he should have asked the then enterprise minister Arlene Foster not to go ahead with it.

He caused a considerable stir when he told the inquiry that civil servants had "got into the habit" of not making proper records of meetings in order to frustrate freedom of information requests because the DUP and Sinn Féin had been sensitive to criticism in the Northern Ireland Executive.

BBC News NI's business correspondent Julian O'Neil profiled Mr Sterling in June 2017 and you can read that here.

It's David Sterling's third visit to Stormont's Senate chamber to give evidence to the inquiry.

Having already been questioned about what he knew and what he did in the early stages of the RHI scheme, today's line of questioning will focus on his involvement in it in his subsequent roles as the chief official in the finance department and as the head of the Northern Ireland Civil Service.

Image source, RHI Inquiry

Given how bruising an experience this inquiry has been for the civil service, Mr Sterling will also have to give answers about what he's doing to sort the organisation out and make sure another RHI-style disaster doesn't happen.

Since his last appearance at the inquiry, he's provided two more witness statements - you'll find them here, external and here, external.

The inquiry's senior counsel David Scoffield QC is asking the questions.

Jayne McCormack
BBC News NI politics reporter

The body that administered the RHI scheme failed to tell a Stormont department of multiple warnings about the potential for the initiative to be exploited, it emerged.

Ofgem had been contracted by the enterprise department to run the RHI.

Image source, Pacemaker

Inquiry panellist Dame Una O'Brien said it was "unbelievable" that Ofgem knew of the scheme's potential risks but had not told Stormont officials.

The inquiry heard of one example of scheme exploitation in England, where sheep farmers were said to be selling their flocks and "raking in money from RHI".

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 major political crisis surrounding the scheme.

The RHI Inquiry began in November last year and Sir Patrick Coghlin (below), a retired Court of Appeal judge, is its chair and has been given full control over how it operates.

Image source, Pacemaker

It is looking 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 autumn 2015
• the scheme's closure in February 2016

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, Pacemaker

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, well beyond a year-and-a-half 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 the initiative 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.

At one point the estimate for the overspend was set at £700m if permanent cost controls weren't introduced - temporary cuts have since pulled the budget back on track for now.

Whatever the scale of the bill, it 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.

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 people 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 the penultimate scheduled day of public hearings at the Renewable Heat Incentive Inquiry.

Returning to the witness chair this morning will be David Sterling, the head of the Northern Ireland Civil Service.

Image source, PA

And Dr Andrew McCormick, another senior civil servant and formerly the top official at the Department of Enterprise, Trade and Investment (DETI), which set up the cash-for-ash scheme, will give evidence later too.

The proceedings begin shortly - you can watch it with us and follow our text commentary.