Ofgem's feasibility study for a Northern Ireland RHI scheme was issued on 16 December 2011, and it pointed out that there was no mechanism in the initiative to control its cost if the uptake was higher than anticipated.

But Mr Aiken points out that at that stage there was no provision for budget control in the Great Britain scheme that officials in Northern Ireland had ignored.

Image source, Getty Images

In DETI's application for EU state aid rules approval for the RHI scheme, it said it was not considering putting a subsidy digression mechanism into the initiative at that stage.

Mr Aiken says that he is unaware of any communication within DETI that led to the adoption of that position, and he says the inquiry will have to establish who decided on it.

On 28 November 2011, the regulations for the Great Britain RHI scheme came into effect and the scheme opened for apllications.

Mr Aiken says there is no overt reference to cost controls, to scheme budget caps, or to digression in the regulations' explanatory notes.

Image source, RHI Inquiry

Sir Patrick makes the point that there is a lack of clarity about the Treasury's involvement of the funding of the scheme.

"It doesn't reflect that well about the communication skill of British departments," he says.

With the consultation on a proposed RHI scheme for Northern Ireland at an end, DETI's Ms Hepper gave Mrs Foster an overview of the responses on 11 November 2011.

Complaints were made by respondents to the consultation that the tariffs on offer were "significantly lower" than in the Great Britain scheme, says Mr Aiken.

A public consultation on DETI's RHI scheme proposals launched in July 2011 is next to come under Mr Aiken's microscope.

He draws the panel's attention to a letter from Peter Hutchinson of the newly-launched renewable heat branch of DETI, which he refers to as the "dear consultee" letter.

Image source, DETI

Mr Aiken says it shows that the Great Britain scheme was assessed as being "inappropriate" for Northern Ireland "with the possibility of over-incentivisation and ineffectiveness".

With a consultation in place, DETI's energy division head Fiona Hepper then made a submission to the minister Mrs Foster for a feasibility study on Ofgem administering the initiative.

"Matters are travelling at pace", says Mr Aiken.

Arlene Foster, the then enterprise minister, told the Northern Ireland Assembly's Enterprise Committee on 21 June 2011 that her department was planning to have an RHI scheme set up for the region by April 2012.

That was "ambitious, given what we now know", says Mr Aiken.

"That indicates that the path was set on the RHI."

It is "rather amusing to see" that concerns about the potential for a perverse incentive in the RHI scheme were raised consistently by those planning the Great Britain initiative but that sense of worry was not shared by DETI, says inquiry chair Sir Patrick Coghlin.

He reminds those in the chamber that the issue was brought to DETI's attention in Octobr 2013 by the so-called concerned citizen Jeanette O'Hagan, as we heard last week.

He says: "The reaction [by DETI officials] to Jeanette O'Hagan, when she suggested such a thing might happen, was: 'People wouldn't do that sort of thing.'"

"Which may be a reflection on the much higher morality of the Northern Ireland population," he smiles.

Mr Aiken says there are a number of points the inquiry may wish to follow up when Mr Lunny undertakes his presentation of the setting-up of the Northern Ireland scheme.

Image source, RHI Inquiry

These include:

• Whether the need for an early review process of the RHI scheme was recognised within DETI
• What needed to be monitored to know whether an early review was required
• Whether a plan was put in place to activate that monitoring
• At what point the proper execution of such a plan should have prompted action

The term "perverse incentive" is one that often crops up in the RHI scandal.

That was a flaw in the scheme that saw claimants being able to increase their payments if the subsidy on offer was higher than the cost of the fuel for their renewable heat system.

The claimant could run their boiler constantly, even if it was not needed, in order to earn more money.

Mr Aiken refers to the DECC policy document that shows Whitehall officials were well aware of the risk of the issue.

He tells the inquiry panel that it will have to assess whether any consideration was give to the perverse incentive by DETI, and if not, why it was not kept in mind.

Inquiry counsel Joseph Aiken picks up from where he left off yesterday, dealing with the Great Britain version of the RHI scheme.

He takes us back to a policy document from March 2011 about the Great Britain RHI scheme, which was set up by the Department for Energy and Climate Change (DECC).

Image source, RHI Inquiry

Mr Aiken demonstrates how "substantial changes had taken place from the original document of 2010".

ln a section on digression, the concept of tariffs reducing for new scheme members after reviews of its operation in order to avoid over-generation, is laid out.

"It is going to be triggered when a preset point is reached so that it wouldn't start prematurely, but equally if uptake was higher than expected digression would start sooner to ensure that costs were controlled," he explains.

BBC News Northern Ireland

Stormont officials removed warnings about a lack of resources available to run the RHI scheme in Northern Ireland almost four years before it was opened, the inquiry heard.

Civil servants at the Department for Enterprise, Trade and Investment (DETI) took the details out of a submission to the then minister Arlene Foster.

The inquiry was also told that the Whitehall department running a similar scheme in Great Britain had done a huge amount of work to prepare for the initiative.

Read our summary from yesterday here, or you can go back over our live updates from that session here.

BBC News Northern Ireland

An independent inquiry into the 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.

Image source, Pacemaker

The RHI Inquiry began this week and Sir Patrick Coghlin (above), a retired Court of Appeal judge, is its chair and has been given full control over how it will operate.

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.

Public and political anger erupted when the scale of the overspend emerged.

The Democratic Unionist Party (DUP) leader Arlene Foster (below) had been the minister in charge of the Stormont department that set up the RHI scheme in 2012, and she faced calls in to stand down as Northern Ireland's first minister in December last year.

Image source, Reuters

She refused, 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.

By doing so, he brought about the collapse of the Northern Ireland Executive. Now, nearing a full 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 - the most recent estimate for the overspend was set at £700m if cost controls are not introduced.

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 massive overspend bill will have to be picked up by the Northern Ireland taxpayer.

Need a quick refresher on what the RHI scandal is all about? Here goes...

The Renewable Heat Incentive scheme - or RHI for short - came to the fore of the Northern Ireland public's minds in autumn last year... and the fallout from the scandal attached to it is still being felt in the region's politics today.

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 damp autumn morning at Stormont as we welcome you to day six of our live coverage the RHI Inquiry.

Today, we'll be hearing more from the inquiry's junior counsel Joseph Aiken, who spoke yesterday about parallels between the separate Great Britain and Northern Ireland RHI schemes.

The rest of the day will be taken up by a briefing from his colleague Donal Lunny on how the RHI scheme came into being.