The RHI scheme was being promoted by biomass boiler firms at agricultural shows and events - one installer told the inquiry in February that the only way someone in those circles couldn't have noticed how lucrative it was would've been if they were "blind and deaf".

Neil Elliott said installers knew of the scheme's flaws soon after it was launched and it was "widespread knowledge" that the incentive was "too good to be true".

Chris Osborne went to those events but says he would've only "very rarely" went into the marquees where boiler firms had their stands set up, promoting the scheme using slogans such as "cash for ash" and "burn to earn".

He says that if he'd gone for a look he would've noticed the scheme being promoted in the terms.

Sir Patrick Coghlin is surprised, saying that given Mr Osborne was a policy man it would've been a "rather basic thing" to get an understanding of how the scheme was working from a commercial point of view.

Mr Osborne claims he did most of his business at those events in the "corridors".

Inquiry chair Sir Patrick Coghlin tells Chris Osborne that the panel is having some trouble with his claim that he had no idea how lucrative RHI scheme was.

He says: "Being an effective policy head, we think we find it somewhat difficult to understand why a) you weren't aware that this was a lucrative scheme; b) if you did become aware you didn't ask: 'How is it lucrative?'"

Image source, RHI Inquiry

He adds that given farming "is not the most generous occupation", one thing farmers "will talk about" is whether there's some way to increase earnings, and he adds: "What is more, they will want their policy director to know about it."

Sir Patrick adds that it's "not easy to understand why a man at the centre of policy perhaps didn't know some of the detail you say you didn't know".

Mr Osborne says he can't explain why he didn't know about the scheme's high returns.

The UFU's Chris Osborne says he was aware from late-2013 that the poultry production giant Moy Park was pushing the RHI scheme to its farmers as part of its expansion plans.

But he says that he wasn't aware that the company was highlighting the big returns available from the scheme.

Image source, RHI Inquiry

His knowledge of RHI developments resulted from "chatter around the edge of the office".

"There was no direct engagement with myself at that stage," he adds, insisting that he never asked any questions of his UFU colleagues, farmers on the ground or Moy Park.

The rates of return on offer from the RHI scheme were massive and an annual booklet produced by the Department of Agriculture and Rural Development outlined the astonishingly short periods of time it took for claimants to recoup their investment in their new heating systems.

In one instance, a pig farmer in County Tyrone stood to recoup the money he'd invested in the space of about 16 months.

Chris Osborne contributed to those booklets with articles on unrelated matters and received copies to read himself and to distribute to others.

But he says he didn't read the RHI-related articles and if he'd done so the high rates of return and payback periods "would've jumped out at me".

Asked if he would've contacted DETI to flag up the scheme's apparent overgeneosity, he says: "In hindsight, I would've maybe picked the phone up and rung somebody to see if that was right".

Inquiry counsel Donal Lunny puts it to Chris Osborne that he was aware of the factors that ought to have made him alarmed about possible over-incentivisation.

The witness says he wasn't alarmed because he wasn't getting that message from DETI and he certainly wasn't getting it from farmers "on the ground".

Image source, RHI Inquiry

Mr Lunny asks if it was likely that farmers would have contacted him to complain that they were being paid too much.

"The number of years I've worked in the agricultural sector, the answer would be 'no'," says Mr Osborne.

Inquiry chair Sir Patrick Coghlin smiles and adds: "I don't think farmers are exceptional [in that regard]."

Chris Osborne accepts that he knew the RHI scheme was attractive to farmers who were intensive users of heat, such as those in the poultry industry.

He also knew that a cost control known as tiering wasn't in place in the RHI - it worked by reducing the amount of subsidy a claimant could receive once their biomass boiler had produced a certain amount of heat.

Asked by barrister Donal Lunny why he wasn't therefore alarmed about the potential for over-incentivisation, Mr Osborne says he believed that once the budget for the RHI was spent the scheme would be suspended.

Image source, RHI Inquiry

But Mr Lunny challenges him on that, pointing out that's exactly what the union had opposed when it first gave its views on the RHI in 2011.

Asked if he should've been concerned by the absence of tiering, Mr Osborne says: "Had we known at the time, yes."

But when Mr Lunny points out that Mr Osborne did know, the witness says he "can't recall" why it didn't cause him concern.

The UFU was opposed to Ofgem administering the RHI scheme because it wasn't based in Northern Ireland.

Ofgem, which had been running the similar RHI scheme in Great Britain, was a London-based body and was chosen by DETI to administer the NI RHI because of its experience in controlling other energy initiatives.

Image source, Getty Images

The UFU informed DETI of its view and Chris Osborne explains that the union felt the scheme should've been operated by "a Northern Ireland-specific agency providing the work".

That's because such an agency would've offered "local responsibility, local knowledge, local jobs".

Asked about a backlog that had developed in approving applications for the NI scheme, Mr Osborne says Ofgem said that was because it didn't have the same number of staff working on it compared with the GB scheme.

The RHI scheme had "broken new ground and opened up a once-inaccessible market and provides an excellent opportunity" for farmers in Northern Ireland, wrote the UFU's Chris Osborne in July 2013.

He wrote a regular column for the News Letter newspaper's weekly Farming Life supplement.

Image source, Getty Images

In one piece comparing a number of renewables schemes, including wind turbines and solar panels, he wrote that the RHI had the "potential to be the most beneficial renewable option for many" farmers.

He concluded his article by writing that the UFU message was that the RHI "provides an excellent opportunity" for farmers.

He tells the inquiry he was also cognisant of the wider intended benefit of the scheme in helping to reduce Northern Ireland's reliance on fossil fuels.

The UFU wanted to see an up-front grants model used for the RHI scheme, rather than an ongoing subsidy offer over 20 years.

Both options were on the table for civil servants to choose and they ultimately opted for the ongoing subsidy option.

The union made its view known in October 2011 in its response - drawn up by Chris Osborne - to DETI's public consultation about the potential RHI.

Image source, Getty Images

In it, he also outlined that the UFU was opposed to the proposal that subsidy levels should be guaranteed for the lifetime of a biomass boiler.

"Anything prolonged into the life of a project could create an uncompetitive sector... and one which is over-incentivised," he wrote.

The UFU was concerned that over-incentivisation wouldn't create a robust and stable renewable energy market.

Asked therefore if the union had known that when the scheme was running it was over-incentivising claimants, it would've been keen to tell DETI about that, Mr Osborne says: "That would be correct."

DETI gave a presentation in September 2011 about its intention to introduce the RHI scheme in Northern Ireland - that was about 14 months before it opened in November 2012.

Chris Osborne attended that event and made notes about what he heard - one note refers to the similar RHI scheme that was running in Great Britain.

"GB RHI would not be apt in NI - danger of over-incentivisation," he wrote.

Mr Osborne says he was aware that DETI was keen to avoid any over-incentivisation in its scheme.

He thinks that was connected to a possibility that the RHI might be offered to the manufacturing industry and there was a fear that the available funding could be used up quickly.

Chris Osborne accepts that it appears the UFU was "in a privileged position" when it was given advance sight of government documents by the then DUP adviser Dr Andrew Crawford.

The inquiry is shown two examples of emails from Dr Crawford on the same day in February 2010 in which he gave Mr Osborne copies of confidential papers ahead of their release to the public.

Image source, Getty Images

Donal Lunny suggests that put the UFU "in a privileged position" and Mr Osborne accepts that it gave him a "heads-up".

Asked if he expected that kind of interaction given Dr Crawford's past employment with the union, Mr Osborne says: "No, definitely not."

He insists it "was not a very regular occurrence".

Chris Osborne is asked about his contact with the DUP adviser Dr Andrew Crawford (below), who's been one of the central figures in the inquiry's investigation.

That's primarily concerned his role as an adviser to Arlene Foster when she was DETI minister and subsequently in the Department of Finance.

Prior to beginning a full-time career in politics, Dr Crawford worked in a policy role at the UFU from 2002 to 2004.

Mr Osborne says there was only a brief overlap in their time at the union - he joined in July 2004 and Dr Crawford left in the autumn that year.

There was never any difficulty in getting information about the RHI scheme from Stormont officials, says Chris Osborne.

The inquiry has heard all about the willingness of civil servants at the Department of Enterprise, Trade and Investment (DETI), which was running the scheme, to give advance notice to industry about impending changes to the RHI.

One of the officials admitted that it was a "naive" thing to have done and he told of his regret.

Image source, RHI inquiry

Mr Osborne says the civil servants "would've been quite accessible" when he had questions about the initiative.

Donal Lunny questions whether the relationship between DETI and the UFU was a "mutually beneficial one", explaining that he's hoping to find out if information the union might've known about the scheme's flaws was passed to the department.

Mr Osborne says that if he'd received a "significant number of calls" about the "problems on the ground... or flaws" he "probably would, in hindsight, have gone to the department and brought it to their attention".

This morning's witness - Chris Osborne of the Ulster Farmers' Union - takes the oath.

The inquiry's junior counsel Donal Lunny is asking the questions.

Image source, RHI Inquiry

Mr Osborne has worked for the union since 2004 and he's a senior policy officer, with his work having included renewable energy matters.

Mr Lunny explains that the witness has been called to the inquiry because he appears to have engaged with Stormont officials who were responsible for the scheme and applicants to it.

Jayne McCormack
BBC News NI politics reporter

Last week, two senior Stormont civil servants gave their views to the inquiry on what led to the RHI debacle.

From "panic time" to "tweeting from the executive room", read our round-up of the key details that were uncovered in the Senate chamber.

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 major political crisis surrounding the scheme.

The RHI Inquiry began in November last year 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 is looking 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 autumn 2015
• the scheme's closure in February 2016

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 DUP leader Arlene Foster faced calls to resign from her role as Northern Ireland's first minister in December 2016.

Image source, Pacemaker

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 the initiative 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.

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 Stormont for what we're assured will be the penultimate week of witness sessions at the Renewable Heat Incentive Inquiry.

The past few weeks have seen a run of civil servants and political advisers in the hotseat but that's all change today with two officials from the Ulster Farmers' Union.

Chris Osborne will be here this morning and Wesley Aston joins us after lunch.

The session starts in few minutes so stay with us for a live stream of the proceedings and text commentary on the important bits.