Ofgem's lawyers had "strong views" on the legal risks that would arise if DETI didn't make the same changes to the RHI scheme that DECC was putting in place in the GB initiative, says Mr Avis.

The administrator advised DETI in a teleconference in June 2012 that it should hold off on opening the scheme until it had made the changes.

DETI decided otherwise, and the minutes of the teleconference record that DETI was "clear that they have a commitment with their minister" to open the scheme by the end of September and "this could not be put back".

Mr Avis tells the inquiry that DETI made it clear "in black and white" that the September deadline had to be met.

In his written statement to the inquiry, Mr Avis says he understood DETI official Peter Hutchinson (below) - who almost single-handedly set up the RHI scheme - to be a legal adviser to the department.

The inquiry has heard a lot from Mr Hutchinson, and while he had a great many roles in the initiative and took on a substantial amount of work in relation to it, seemingly due to a lack of support and resources, he certainly wasn't a legal adviser and has never claimed to be.

Image source, RHI Inquiry

Asked why he believed Mr Hutchinson was a lawyer, Mr Avis says he was "feeding in comments quite specifically".

He says that when he was writing his statement to the inquiry his recollection was that Mr Hutchinson was a legal expert but he adds: "Clearly if that's not the case I stand corrected."

DETI intended that its RHI scheme for Northern Ireland should closely mirror a similar initiative operating in Great Britain, including adopting the operating regulations from the GB scheme.

But by June 2012 problems had emerged with the GB scheme's regulations, and the Department for Energy and Climate Change (DECC) - which was running it - had decided to make changes, including adding cost controls.

Image source, RHI Inquiry

Ofgem lawyer Marcus Porter (above), who appeared at the RHI inquiry in January, was unhappy that DETI wanted to press ahead without adopting the updated GB regulations, and instead deciding to make the necessary amendments in future.

He suggested to his boss that DETI may want to "take on an avoidable legal risk", but that didn't mean that Ofgem had to follow suit.

And that's pretty much the point where today's questioning of Mr Avis begins.

First up before the inquiry this morning is Keith Avis - he was the manager at the administrator Ofgem who was responsible for the RHI scheme from April 2012 to February 2013.

His team's role was to put in place the procedures for the operation of the scheme.

Image source, RHI Inquiry

Mr Avis has already appeared before the inquiry - he was here at the end of in January and you can find our report of his evidence here.

His written statement is also available, external on the inquiry's website.

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

BBC News Northern Ireland

The head of the Northern Ireland Civil Service admitted to the inquiry that meetings between Stormont ministers and their staff were sometimes not minuted in order to frustrate freedom of information requests.

David Sterling, who was the permanent secretary of the Department of Enterprise, Trade and Investment (DETI) when the RHI scheme was being set up, said the practice of taking minutes had "lapsed".

Image source, Press Eye

He said the DUP and Sinn Féin were sensitive to criticism when they were in government and civil servants had therefore "got into the habit" of not recording all meetings.

Mr Stering said this was done on the basis that it was sometimes "safer" not to have a record that might later be released to the public under freedom of information legislation.

BBC News Northern Ireland

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, EPA

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 aren't 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... and 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.

Its a wet aul' morning up here on Stormont hill, so we're glad to be inside beside a radiator as we take in another session of the Renewable Heat Incentive Inquiry.

After yesterday's revelations from David Sterling, the head of the Northern Ireland Civil Service, we'll be hearing from the RHI scheme's administrators today.

Keith Avis and Marcus Porter from Ofgem will be appearing in the witness chair, and we'll bring you a live video stream of proceedings as well as the usual detailed text commentary.