It was "very odd" for the changes to the RHI scheme in autumn 2015 to be announced by DETI before they had been agiven approval by the Department of Finance, says Emer Morelli.

Image source, PA

She refers to her experience on working on policy in the civil service, explaining that the approval process "is there... for a reason".

She says that before a policy is set it's essential to "get it right", adding: "Once it's in the public domain... it's hard to revoke and come back from."

DETI had been discussing its planned changes to the RHI scheme with the energy and agri-food industries in the summer of 2015 before they had even been approved by the finance department.

By the time finance officials saw the plans in October, the had already been publicly announced and Emer Morelli says that by that stage the ship "had very firmly sailed".

Inquiry barrister Joseph Aiken suggests that finance officials were being "backed into a corner, whether intentionally or otherwise" - using the ship reference, he says they had to decide whether to "blow it up or let it go".

Ms Morelli says the explosive option wasn't available because if the finance department had intervened that would've delayed the introduction of crucial cost controls.

DETI told the finance department in July 2015 that there would be a need for a change to legislation for the RHI scheme.

"It is not possible to cease, suspend or otherwise delay applications without assembly approval, which would take at least three months," it said.

Image source, RHI Inquiry

Joseph Aiken notes that stopping or suspending the scheme didn't appear in DETI's subsequent business case: "What's in it is tiering (of the scheme tariff) and expansion of the scheme."

Emer Morelli says she doesn't think DETI followed the course of action that it said it would.

Civil servants at DETI told their colleagues in the Stormont finance department at the start of July 2015 that they'd been spending money through the RHI scheme without the proper approval.

But they claimed that they'd carried out a review of the scheme, as had been required in the conditions of the original approval for the initiative, in October 2013 - that wasn't true because a review hadn't taken pace.

By that stage, big financial cracks had appeared in the scheme and DETI was attempting to get a handle on the spending on it by trying to add cost controls.

Emer Morelli tells the inquiry that what DETI was telling her department at the time gave her no indication that "this was a scheme that was out of financial control".

But she says she accepted what DETI was saying and she didn't dig deeper.

There was much confusion within the Department of Finance about the RHI scheme and the inquiry has heard that its officials spent an "inordinate amount of time" trying to understand it.

They met civil servants working at the Department of Enterprise, Trade and Investment (DETI), which set up the scheme, in mid-June 2015 in an attempt to get their heads around it.

Image source, Getty Images

But even a couple of weeks later, at the end of that month, finance officials were still struggling - inquiry barrister Joseph Aiken says there "appears to have been a complete misunderstanding" of how the scheme was funded.

Emer Morelli accepts that her officials "didn't know" and she says she concedes that they should've asked questions earlier.

Emer Morelli, the head of supply at the Department of Finance, took the oath at her first witness session on 26 June so it's straight into the questions.

The inquiry's junior counsel Joseph Aiken will be on the floor today.

Image source, RHI Inquiry

Back in June, Ms Morelli accepted that finance officials should have taken more care to establish how the RHI scheme's budget worked and she admitted that assurances were taken "at face value".

Mr Aiken explains that the inquiry will be use today to look at the Department of Finance's role when difficulties became apparent with the scheme in the summer of 2015.

That culminated in the department's involvement in producing an addendum business case for the non-domestic scheme in October of that year.

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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 will operate.

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 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, 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 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 proper autumn morning on the Stormont estate as we prepare for day 101 of the Renewable Heat Incentive Inquiry.

Today's witness, Department Of Finance official Emer Morelli, was last at the inquiry back in sunny June, when she said civil servants were "too hands-off" in accepting assurances over the financing of the failed energy scheme.

Today's session starts shortly - stay with us for live stream of the proceedings and text reporting of the most important bits.