Dr Crawford's brother James received a quote in June 2014 from a boiler installer that outlined that he stood to make £250,000 from the RHI scheme over its 20-year lifetime.

The inquiry barrister Mr Aiken asks whether James Crawford ever showed him the quote and said: "surely that can't be right?"

Image source, Getty Images

At the time Dr Crawford was an adviser to the enterprise minister and he was well aware of the RHI scheme but he witness says they never discussed the quote and he has "no recollection" of ever having seen it.

In January 2015, James Crawford got another quote - this time from a different boiler installer - which stated that the RHI scheme would provide an income of £24,000 a year and the boilers would therefore be paid off within three years, leaving the income over the remaining 17 years on the scheme as a big bonus.

Again, Dr Crawford insists he didn't see it.

Dr Crawford's brother James runs a company that installed boilers through the RHI scheme.

James Crawford bought a field from Dr Crawford and set up a poultry farm on it but the witness says: "There's no financial link between myself and my brother in any way."

Dr Crawford's cousin Richard Crawford has six boilers registered on the RHI scheme and another cousin John Crawford has three boilers on the initiative.

The Stormont executive's then press secretary David Gordon (below) - a former editor of The Nolan Show - was involved "briefing against me to the media" in January 2017, claims Dr Crawford.

He say he has no proof but is basing his claim on email exchanges that have been give to the inquiry.

"If you look at the exchanges that took place between him and [DUP adviser] Richard Bullick in December [2016] you see the reference to 'getting the real story out'," he adds.

Asked if it was clear to him that the DUP's alleged "targeting" of him was because of delays to adding cost controls to the RHI scheme rather than the involvement of his relatives in the poultry industry Dr Crawford says his family's position was already well known at that point.

Dr Crawford entered "the middle of a media spotlight in terms of... who was to blame" for the RHI scandal in mid-January 2017, he says.

The DUP "started to get media queries" late on the evening of 17 January and he became aware that BBC Radio Ulster's The Nolan Show was intending to name him as the person who had tried to delay cost controls.

The party drew up a statement, which Dr Crawford asked to be amended to say that he didn't want cost controls delayed.

He was then told by a DUP adviser colleague that the Department of Enterprise, Trade and Investment's (DETI) permanent secretary would be naming him in a Northern Ireland Assembly committee hearing as the man behind the cost controls delay.

After that, he says he went to see DUP leader Arlene Foster at her home and offered his resignation, which was accepted.

He was also told that fellow DUP adviser John Robinson was likely to resign too because he hadn't declared that his father-in-law was a claimant on the RHI scheme.

Dr Crawford says he's "always been sore" about the way the DUP handled the RHI scandal when it erupted publicly in December 2016, claiming that the party tried to "pin the blame" on him.

Dr Andrew McCormick, who was the most senior civil servant in Stormont's enterprise department, says in his witness statement that in December 2016 Mr Johnston asked him to look up details of two of Dr Crawford's relatives who were claimants on the RHI scheme.

Dr Crawford says he didn't know that had happened and adds that nobody from the DUP who was looking into the RHI debacle at the time asked him about his involvement.

Image source, RHI Inquiry

Sir Patrick puts it to him that both he and fellow DUP adviser Cairns appear to be saying they were "hung out to dry" by the party.

The witness, who still works for the DUP in an part-time advisory role, says he was "blamed unfairly" and believes that "work was going on behind the scenes to basically pin the blame on me if possible" in December 2016 and January 2017.

Sir Patrick puts it to the witness that he and Mr Cairns both feel they were the "fall guys" because they "did not fit the narrative".

Mr Aiken quotes from Mr Johnston's evidence that Dr Crawford has always denied seeking to delay the introduction of cost controls in the RHI scheme.

"Andrew Crawford as been known to me for many years as a valued colleague who sought to do his best to make the mandatory system work," says Mr Johnston in his statement.

Image source, RHI Inquiry

Inquiry chair Sir Patrick Coghlin (above) fails to see the relevance of bringing that up as it's simply the view of one individual about another.

"It's a decision for this panel whether Dr Crawford or Mr Johnston, Mr Cairns is telling the truth," he says.

Dr Crawford has already taken the oath so Mr Aiken (below) gets straight into contradictions in the evidence offered by the witness and by his fellow former DUP adviser Tim Cairns.

Mr Cairns said during his evidence over the past two days that Dr Crawford had been working with him on trying to get cost controls for the RHI scheme delayed in the autumn of 2015.

Image source, RHI Inquiry

But Dr Crawford has previously stated in his evidence that "at no stage" did he "seek to delay the introduction of cost controls".

He's also said that at no time did he and senior DUP adviser Timothy Johnston discuss, let alone agree a party view about how Stormont's enterprise department and its minister Jonathan Bell should proceed regarding the RHI in the summer of 2015.

A son of a farmer from Beragh in County Tyrone, Dr Andrew Crawford was the trusted adviser to Arlene Foster during much of her time as a Stormont minister and he had a significant input in parts of the RHI scheme.

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 Dr Andrew McCormick in January 2016 as the adviser who exerted influence to keep the scheme open - Dr Crawford resigned as a DUP ministerial adviser shortly after that but denied the claim and said he had "acted with complete integrity".

During his time advising Mrs Foster, he had access to all of the internal material related to the scheme and he twice sent confidential papers about it to his poultry farmer cousin, who is claimant on the initiative.

When quizzed about that at the RHI Inquiry, he insisted that it had not been his intention to give his relative an advantage but he acknowledged that "it was wrong - I shouldn't have done it".

He denied that he had a "widespread habit" of leaking government documents.

Image source, RHI Inquiry

Back for his seventh day in the witness chair, Dr Andrew Crawford will be questioned by the inquiry's junior counsel Joseph Aiken.

Dr Crawford has provided four witness statements to the inquiry - you can find all of them on the inquiry's website, external.

Jayne McCormack
BBC News NI politics reporter

A former DUP adviser who resigned at the height of the RHI scandal has told the inquiry that he may have been "expendable" while other party advisers may not have been.

Dr Andrew Crawford (below) was an adviser to Arlene Foster in the enterprise department when the RHI scheme was set up but he resigned after claims he had exerted influence to delay cost controls.

The inquiry has heard claims that he and fellow DUP adviser Timothy Johnston were involved in seeking to delay the introduction of reduced subsidies.

Ahead of his appearance at the inquiry today, Dr Crawford says in his witness statement, external that he never suggested a delay to anyone and that he would not have felt it appropriate to do so.

Jayne McCormack
BBC News NI politics reporter

There's an "irreconcilable difference" between two former DUP advisers and their accounts about which of them sought to delay the addition of cost controls to the RHI scheme, said the inquiry chair.

The remark came from Sir Patrick Coghlin during Tim Cairns' (below) second day at the RHI Inquiry.

Image source, RHI Inquiry

Mr Cairns claimed that he was told by Dr Andrew Crawford to seek the latest possible date for cost controls to be imposed.

But Dr Crawford has said that the decision to try to postpone their introduction was Mr Cairns' alone.

BBC News NI

It is the scandal that sent Northern Ireland's devolved government up in flames and risked leaving taxpayers hundreds of millions of pounds out of pocket.

The RHI debacle has exposed serious flaws in the region's civil service and governance systems.

BBC News NI has followed every minute of the inquiry into the scandal since it started last autumn.

Read our review of some of the major revelations that have emerged so far.

BBC News NI

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, well beyond a year-and-a-half 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.

At one point the estimate for the overspend was set at £700m if permanent cost controls weren't introduced - temporary cuts have since pulled the budget back on track for now.

Whatever the scale of the bill, it 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.

There's been no let up in the fascinating insights provided by the witnesses at the Renewable Heat Incentive (RHI) Inquiry over the past 10 days here at Stormont's Parliament Buildings.

And today could bring more, with the return of one of the central figures in the RHI story.

Dr Andrew Crawford was an adviser to the former enterprise minister Arlene Foster and his previous evidence sessions have proved to be most revealing - let's see what emerges today.

The action starts shortly and we'll have a live stream and a text commentary of what Dr Crawford has to say.