Shortly before the June 2011, the consultancy firm Cambridge Economic Policy Associates (CEPA), which had been engaged by DETI to draw up a economic assessment of the options for the RHI scheme, delivered its final draft report.

Dr Crawford says he believes that "no report was discussed in detail" during the meeting involving DETI officials and the minister, during which the future of the scheme was decided.

Image source, RHI Inquiry

"I don't believe any report was discussed at all outside the contents of the submission that was presented to us before the meeting", he adds.

And he says that no copy of the draft final report was left for him and the minister to consider.

"I do not believe there was any additional information brought to the meeting or discussed at the meeting to change the direction of travel that was in the submission."

When the RHI scheme was presented to Dr Crawford and Mrs Foster it was "complete new territory" to them, he says.

He had "no expertise" in the area and he wasn't across the "nuts and bolts" of how it would work - instead, his focus was on its affordability.

Image source, Getty Images

It "was not my role to second guess what officials were putting up to us in paperwork", he says, and he "believed that to be accurate".

As it turned out, the details from civil servants in the submission to Mrs Foster outlining the options for the RHI scheme was inaccurate.

Dr Crawford claims that DETI's energy boss recommended an ongoing subsidy scheme as the model for the RHI scheme at a key meeting involving the minister in June 2011.

Two main options were on the table - the ongoing subsidy model and an up-front grants offer, which would've been much better value, and the first of those was ultimately selected by Mrs Foster.

Mrs Hepper has told the inquiry that she didn't express a preference and nor was she asked for one.

Dr Crawford disagrees with her version of events and says that there was a "clear recommendation" from civil servants that the subsidy offer was their preference.

Image source, RHI Inquiry

He spent a couple of days in the hotseat last week and now Dr Crawford returns to the Senate chamber.

He's already been sworn in so it's straight into the questions from the inquiry's junior counsel Joseph Aiken.

Mr Aiken says he wants to start by picking up on the lengthy questioning with Mrs Foster last week on the vital meeting she and Dr Crawford had with the head of the Department of Enterprise Trade and Investment (DETI) - Fiona Hepper in June 2011.

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 said an accusation against him "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.

Image source, Pacemaker

He also said that a key decision that "set the direction of travel" for the scheme ought not to have been taken.

He accepted that he had not "protected his minister" Mrs Foster because he had not queried inaccurate information she had been given.

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".

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.

It's a wonderfully sunny start to the week up here on Stormont hill and we hope it's the same where you are too.

We're here at Parliament Buildings for another week of evidence from two of the star witnesses at the Renewable Heat Incentive (RHI) Inquiry.

Image source, Reuters

The Democratic Unionist Party (DUP) leader and former first minister Arlene Foster will be here on Wednesday and Thursday to follow up her appearances last week.

But first we'll be hearing from Dr Andrew Crawford, who was her adviser during her time as Stormont's enterprise minister - proceedings will get under way shortly.