Ms Wheeler became more involved in the RHI scheme in September to October 2011, when she considered the draft RHI provisions for DETI.

Mr Lunny asks her what her understanding was regarding the role of Arthur Cox.

Image source, RHI Inquiry

"I just assumed that they were providing the advice on the energy aspects, the technical aspects of the scheme," she says.

"I didn't actually think overly of what they were doing - I just concentrated on my role, which I viewed as being more the legislative side of it."

Ms Wheeler was a solicitor in the DSO, which gave legal advice to Stormont departments.

Between May 2011 and October 2012 she dealt with a number of legal arrangements of the RHI scheme, including draft regulations and the arrangements between the Department for Enterprise Trade and Investment (DETI), which set up the scheme, and the administrators Ofgem.

Image source, RHI Inquiry

Mr Lunny explains why the legal firm Arthur Cox was engaged to assist DETI with the legal aspects of the RHI scheme.

"DSO advisory lacked the specialist energy legal knowledge and expertise to provide all of the advice that DETI were likely to require," he explains.

Nicola Wheeler from the Departmental Solicitors Office (DSO) takes the oath to begin her evidence.

The DSO is the in-house legal service for Northern Ireland Executive departments and other non-departmental bodies.

Image source, RHI Inquiry

The inquiry's junior counsel Donal Lunny runs through some of Ms Wheeler's written evidence and they agree certain clarifications she wishes to make.

The statement submitted to the inquiry from Ms Wheeler and Claire Archbold is available here, external.

BBC News Northern Ireland

An independent inquiry into the RHI scandal was established in January 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 operat

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 last year.

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. We are now a year on and Northern Ireland remains without a devolved administration.

There were critical flaws in the way the RHI scheme was set up that left it open to abuse and that later saw its budget spiral out of control.

Crucial cost curbs that existed in a similar scheme in Great Britain were not replicated and claimants could effectively earn more money the more fuel they burned.

That was because the subsidies on offer for renewable fuels were far greater than the cost of the fuels themselves.

As a result, the scheme racked up a projected overspend of hundreds of millions of pounds and the 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 autumn 2016.

Few people, if anyone, would have expected it to have the consequences it has done in the months that followed.

Image source, Getty Images

It 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.

Welcome along to our coverage of the Renewable Heat Incentive Inquiry from Stormont on this Tuesday morning.

Today we'll hear from Stormont's Departmental Solicitor's Office and the law firm that was tasked with drawing up the regulations of the RHI scheme.

Just worth noting that today marks a year since Sinn Féin's Martin McGuinness resigned as Northern Ireland's deputy first minister, in part due to the scandal surrounding the RHI scheme.