According to Mrs Hepper, she went through the submission paragraph by paragraph with Mrs Foster and went through the key figures about the RHI scheme in detail.

The figure would've shown that the subsidy model that was eventually chose for the initiative was not the best option, working out much more expensive by at least a couple of hundred-million pounds.

Image source, EPA

Mrs Foster's account is different - she says in her written statement to the inquiry that it's "highly unlikely that she took me through it in detail".

Dr Crawford says that if Mrs Heppr's account is accurate she "would've been asked to redraft the submission so that what she was saying verbally... was being reflected" in the paper.

The all-important meeting involving DETI civil servants, Mrs Foster and Dr Crawford on 14 June 2011 that resulted in the minister deciding to proceed with the RHI scheme comes under the microscope.

But the lack of any written record from the meeting has left the inquiry in a serious quandary, having to piece together what happened in the room from follow-up emails and witnesses' evidence.

Image source, RHI Inquiry

DETI's then energy boss Mrs Hepper has had her say on what took place and it's fair to say that Dr Crawford's memory of the event is different.

Mrs Hepper has told the inquiry she was "quite clear" with the minister about how the scheme would be funded but Dr Crawford disagrees, saying that if it had been mentioned it would've had "a major implication on the decision that was taken at that meeting".

Dr Crawford - Mrs Foster's ministerial adviser - says he can't remember giving her any advice concerning the key submission that led to the "direction of travel" on the RHI scheme before she met DETI officials to discuss it.

Image source, Getty Images

He says he doesn't believe he gave the minister any pointer that would've differed from the contents of the document that civil servants had drawn up.

"When an official was coming up they were the person to provide clarity and whatnot, so it wouldn't have been normal for me to provide comments," he adds.

Dr Crawford says he doesn't know why the officials "were so adamant on driving through" an ongoing subsidy model for the RHI scheme and Mrs Foster was not pushing for it.

The witness says his assumption is that there was already a lot of work being done on the scheme - "that they were already pre-planning it".

Image source, RHI Inquiry

If the minister had started changing it that would have cause a lot of extra work for the civil servants, he adds.

He says he "can see no other rationale" why the submission did not follow the work being done by the expert consultants at CEPA.

The submission sent to Mrs Foster outlined options for which model the minister should chose for the RHI scheme.

Dr Crawford says there was a "clear steer" that the 20-year incentive scheme which was ultimately chosen was DETI's "preferred option".

But it was much more costly than another option - an up-front grants model - that was presented to the minister.

Also in the submission is a section on the subsidies on offer through the scheme, indicating that it would be 1.4p per kWh on heat produced - lower than the equivalent tariff in the GB RHI scheme - and it would later rise to 5.9p.

Mr Aiken asks the witness if he would have been "any the wiser about any of this".

Dr Crawford says he would purely be looking at the relative figures between NI and GB but he wouldn't have looked at "whether it was good, bad or indifferent".

Image source, RHI Inquiry

DETI's then energy boss Mrs Hepper (above) was considered to be a "capable civil servant" who work was considered to be "accurate", says Dr Crawford.

She was the official who sent the key submission to Mrs Foster that's been discussed at length this morning.

When she submitted papers to the minister Dr Crawford says he would've "run a less critical eye over it" than he might've done in the case of papers that came from other officials.

Inquiry chair Sir Patrick Coghlin wants to know about Dr Crawford's reaction to the reference in the submission that there were "issues to be addressed" in the CEPA report.

He asks: "Did the minister not say to you: 'Dr Crawford, there are a number of issues that need to be addressed, shouldn't we be looking at those?'"

Image source, RHI Inquiry

The witness says he can't recall whether that discussion took place or whether the minister said that or not

He says that when they both received the submission they were told there would be a meeting with head of DETI's energy division Fiona Hepper to discuss the technical aspects of the scheme.

"When a submission comes up like this you do not expect to have to interrogate the paperwork behind it to be sure that the submission is accurate," he adds.

Dr Crawford says civil servants should never have sent the submission about the RHI scheme in June 2011 to Mrs Foster because there were "too many issues to be resolved" with the economic report on which it was based.

It's now known that the submission was flawed and contained inaccurate information.

Image source, Getty Images

"It was not appropriate for either the submission to come up or the meeting to take place," says Dr Crawford.

He adds that the contents of the submission and the report were "at such odds with each other" and if he had known his advice to Mrs Foster "would have been to start again".

On 8 June 2011, a submission was made to the minister Mrs Foster ahead of a meeting on 14 June later when the important decision was taken on what model to choose for the RHI scheme.

But officials at Mrs Foster's Department of Enterprise, Trade and Investment (DETI) still had serious questions about an economic appraisal report by the external consultancy firm Cambridge Economic Policy Associates (CEPA), which was still in draft form, and on which the RHI scheme was based.

Image source, Getty Images

In spite of this, the submission went ahead with a note that "there are a number of issues to be addressed before the report can be finalised".

CEPA replied to DETI's concerns, identifying 56 concerns that had to be addressed - that response came on 15 June, the day after meeting with the minister.

Matters begin with a return to some intriguing evidence Dr Crawford gave yesterday when he said that nationalist parties had a reluctance in allowing Northern Ireland to join UK-wide projects when the issue at hand could be devolved to Stormont.

In the case of the RHI scheme, Stormont set up its own instead of joining a nearly-identical initiative that was already running in Great Britain and some witnesses have told the inquiry in retrospect that that wasn't a good idea.

Mr Aiken digs out evidence from the RHI scheme's administrator Ofgem dating back to 2011, when an official noted that the Stormont department running the initiative said "some local political issues" could impact on how the initiative would work and there was an "imperative to differentiate" its initiative from the similar one in GB.

Image source, PA

Mr Aiken says that shows that civil servants also had on their mind the political sensitivities that Dr Crawford referred to yesterday.

But Dr Crawford adds: "At no stage would the minister have said: 'Make tweaks to the scheme for the sake... so it's a Northern Ireland scheme, not a UK-wide scheme.'

"Before the minister could decide to just adopt a UK scheme she had to take into account of the political implications that would have to be discussed at the executive."

Image source, RHI inquiry

Dr Crawford has already taken the oath so we're straight into the action, with the inquiry's junior counsel Joseph Aiken once again asking the questions.

BBC News Northern Ireland

Arlene Foster's former ministerial adviser said he did not try to keep the RHI scheme open as it ran out of budgetary control in 2015.

He was referring to an accusation that was made against him by a senior Stormont civil servant in January last year, which led to Dr Crawford's resignation soon afterwards.

He said the claim "runs contrary to what I was doing at that time" and he had provided the inquiry with evidence that proved he had not been seeking to keep the scheme open.

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, 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 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.

Welcome to Thursday's live coverage of the Renewable Heat Incentive (RHI) Inquiry from Stormont's Parliament Buildings.

It's fair to say that all eyes will be on this afternoon's session when we'll be hearing from Democratic Unionist Party (DUP) leader Arlene Foster, who was enterprise minister when the RHI scheme was being set up and initially run.

But we've still got to hear more from her former special adviser Andrew Crawford, who began his oral evidence yesterday.

The session starts shortly so stay with us for what promises to be a fascinating day.