Mr Aiken is scrutinising the DETI correspondence on the non-domestic scheme. In this correspondence, a list of main issues to be addressed, cost control does not feature.

However, further down the correspondence, it says that it may be appropriate to review existing tariffs.

Mr Aiken asks whether that would have caused Dr Crawford concern that there was a "lurking issue that been uncovered over RHI".

Image source, Getty Images

"Not concerned because it wasn’t being flagged up as an issue to be concerned or that we were going to run out of budget or anything like that," says Dr Crawford.

He adds that the next paragraph in the correspondence was about encouraging more people to apply for the scheme.

"It may have given me a false sense of security," says Dr Crawford.

Mr Aiken turns to the theme of pressure building to deliver on the domestic RHI scheme.

UUP MLA Sandra Overend had made a query on behalf of a constituent on the introduction of the domestic scheme.

The public consultation for that scheme closed in October 2013 and it was planned to open in April 2014.

Image source, RHI Inquiry

John Mills (pictured above), the head of the energy division at the time, responded to say that an announcement would be made on the scheme shortly.

"If we’re going to launch the scheme we want to know how long shortly was. It was more to try and nail down when this scheme is going to be launched," says Dr Crawford.

DETI officials delivered a submission to the minister preparing her for a briefing to the assembly's Enterprise Committee in January 2014.

It did not contain CEPA's warning that the scheme would never achieve its 10% target.

Image source, RHI Inquiry

"In fact, the internal briefing for the minister gives the impression that it can't be known what the position is and its going to have to be monitored," Mr Aiken observes.

Dame Una O'Brien is questioning the comparison between the NIRO scheme and the RHI scheme.

"You are a special advisor, did you not understand the different mechanisms between the schemes," she asks.

Dr Crawford says he did, that one scheme was on-grid, another was off-grid. "They were totally different beasts," he says.

Image source, Getty Images

Dr MacLean makes the point that with the NIRO scheme, it was paid for by consumers. This scheme exceeded its budget and levy controls were introduced later on.

Mr Aiken turns to an oral question that was put to minister Foster by Stephen Agnew, leader of the Green Party.

He posed a question about the uptake of the RHI scheme.

In a briefing document provided in response, the RHI scheme is said to be "performing favourably compared to Great Britain", but that predicting whether the scheme would reach target was difficult because there was no centralised collection of up-to-date data".

Dr Crawford explains that the issue of predictions of uptake were an issue when the Northern Ireland Renewables Obligation (NIRO) scheme was established.

This is an environmental scheme to encourage the use of renewable electricity in Northern Ireland. Under the scheme, generating stations with a capacity of 50kW or less are termed ‘Micro-NIRO’ stations.

Mr Aiken raises the atter of the CEPA (Cambridge Economic Policy Associates Report) of June 2013.

The whole point of the RHI scheme was to attain a target of 10% renewable heat by 2020.

CEPA had reported that whatever DETI did they were not going to achieve the 10% target

Image source, Getty Images

Mr Aiken asks the witness whether he was ever made aware of this.

"It doesn't spring to mind - me being told the 10% target was going to be impossible to reach," Dr Crawford says.

Image source, RHI Inquiry

After a bit of back and forth on timelines between Mr Aiken and Sir Patrick, finally, someone breaks through the heavy questioning with a joke!

"It's all coming together Dr Crawford," says Mr Aiken, smiling at the witness.

"Well, let's not rush," warns Sir Patrick.

The chamber laughs and even Dr Crawford unfolds his crossed arms.

But when the questioning being again Dr Crawford's arms are firmly crossed again.

Dr Crawford insists that the DETI civil servants did not communicate the importance of budget management issues.

"At no stage did officials elevate the importance of cost controls," he says.

"That was not being flagged up to either the minister or myself," he adds.

Image source, RHI Inquiry

Panel member Dame Una O'Brien is surprised that Dr Crawford would not have read a letter from the GB minister for energy.

"It would have seemed to me to be one of the first documents you would have reached for," she says.

Dr Crawford says that if any such letter attached to a submission he would have read it.

He says there was a very heavy workload in the department at the time.

Image source, RHI Inquiry

Mr Aiken is drawing Dr Crawford out on the letter accompanying the submission from minister Barker.

"It would be odd if you were receiving a draft reply and someone of the ilk of minister Foster or yourself didn’t say, 'The letter isn’t here, can I have a copy of it?'" says Mr Aiken.

He also asks him what this might say to the inquiry about the subject of cost control, and whether minister Foster had been aware of the importance of cost control.

"It wasn’t brought to the minister’s attention as an important issue either before this time or during this period," says Dr Crawford.

"It wasn’t a submission and it should have come up as a set alone submission before this period and again this should have been reinforced and included in response to this letter to Greg Barker. That did not happen in this case."

Keeping with the letter from minister Barker, Dr Crawford makes the point that he is unclear whether that letter was attached to the submission proposing a draft response.

Dr Crawford says he does not remember whether the letter was attached or if he asked to see the letter at the time.

Image source, Getty Images

"I can’t confirm or deny whether I asked to see it or not," he says.

Sir Patrick is critical of this, saying: "How can you have a system in which a minister is given a draft response to a letter that she hasn’t read or hasn’t seen?"

"That’s what I can’t confirm whether she had seen it or not," says Dr Crawford.

Mr Aiken, counsel for the Inquiry, is asking Dr Crawford about correspondence sent from the then UK government's then energy minister Greg Barker.

Mr Barker - now Lord Barker of Battle - talks in this correspondence "in considerable detail" about budget management, says Mr Aiken.

Asked whether Dr Crawford had picked up on the need for cost control he responds: "Clearly I didn’t pick it up or I would have annotated the submission and asked for more detail on that particular point."

Image source, RHI Inquiry

Sir Patrick Coghlin pushes him on this, asking what more detail he would have asked for.

Dr Crawford says: "I would have asked for more detail on the issues that were raised in terms of the Barker and the content of his letter himself."

Image source, RHI Inquiry

Dr Crawford is ready to begin the session.

You can see his written evidence here, external.

Since Dr Crawford has already been sworn to tell the truth we can go straight into the questioning.

Asking the questions today is inquiry junior counsel Joseph Aiken.

A son of a farmer from Beragh in County Tyrone, Dr Andrew Crawford is a former employee of the Ulster Farmers' Union.

He was an assistant to the former DUP MEP Jim Allister before the North Antrim politician quit to form the Traditional Unionist Voice.

Dr Crawford was an adviser to Arlene Foster when she was enterprise minister during the time the RHI scheme was created, and followed her to the Department of Finance and Personnel.

Former DUP minister Jonathan Bell accused him of preventing the closure of the scheme, but Dr Crawford denied that.

He was also named by senior civil servant Andrew McCormick, in a hearing of the Northern Ireland Assembly's Public Accounts Committee, as the adviser who exerted influence to keep the scheme open - although Dr McCormick said he had no evidence for his claim.

Dr Crawford resigned as a DUP ministerial adviser shortly after that but denied Dr McCormick's claim and said he had "acted with complete integrity".

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.

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.

Image source, AFP

Welcome to a warm and sunny Stormont - a strange day to be discussing 99kW heating boilers perhaps.

We're primed for a fascinating session tody with the return of former DUP special adviser (SPAD) Dr Andrew Crawford.

Dr Cawford has been here several times before, and there were some sharp exchanges between him and inquiry chair Sir Patrick Coghlin back in April.

Stick with us for live video and updates throughout the day.

The session kicks off at 09:45.