Mr Aiken asks how Mr Poulton would have gained the necessary technical knowledge when he took over responsibility for a RHI scheme, given his generalist background.

"It's a balance - I think you're reliant to the people that are on your team to be the technical experts, and they are employed as such," he replies.

Image source, RHI Inquiry

He says his role at the beginning of the scheme was not so much to understand the technical details but to make sure it was delivered on time and on budget.

Ofgem's arm that was dealing with the administration of energy schemes was growing quickly when he was there - it has 300 employees but that figure was between 200 and 220 when Mr Poulton started there.

Chris Poulton begins by affirming that he'll tell the truth and the inquiry's junior counsel Joseph Aiken begins the questioning.

Mr Poulton, who says he has an "underused" biology degree from Warwick University, worked as the head of operations for a mobile phone network before he joined Ofgem in January 2014 as its deputy managing director.

After about 12 months in the role, he was promoted to acting managing director, a role he held until his departure from Ofgem this year.

Image source, RHI Inquiry

Ofgem administered the RHI scheme for DETI, the Stormont department that set up the initiative.

Mr Poulton's written statement to the inquiry is available here, external.

He's already made a visit to Stormont's Senate chamber, where the inquiry is being held - he faced a testing afternoon before the Northern Ireland Assembly's Public Accounts Committee to answer questions on the RHI debacle in October 2015.

At the end of that session, the committee chair Robin Swann told Mr Poulton and his colleagues: "We've been sitting here for nearly four-and-a-half hours and I think you've actually raised more questions than you've answered."

A former head the team that was running the RHI scheme revealed he commissioned a vital document that outlined potential concerns with the initiative but didn't read it when it was produced.

John Mills, the energy boss at Stormont's Department of Enterprise, Trade and Investment (DETI) claims he asked one of his civil servants Peter Hutchinson to put together a handover note before he moved to another job.

Image source, Pacemaker

The handover outlined the work that had to be done on the scheme and included "immediate actions" that Mr Hutchinson felt had to be addressed.

Mr Mills told the inquiry he can't remember seeing the handover or reading it and assumed that staff working in his team flag up any serious issues contained in it.

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 are not 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.

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.

Image source, Reuters

It's another cracking morning for the dog-walkers and runners at the Stormont estate.

We're all poised for a sunny weekend but in the meantime there's the small matter of another day's live coverage of the Renewable Heat Incentive (RHI) Inquiry.

Today we'll be hearing from Chris Poulton - until recently he was the acting managing director of the part of Ofgem that dealt with the administration of the RHI scheme.

Our live stream and commentary begins shortly - stay with us throughout the day.