It's been a most enlightening afternoon at the inquiry.

Sir Patrick assures Ms Clifton that she shouldn't need to return, but we'll be seeing one of her Ofgem colleagues - Dr Edmund Ward - in the hotseat tomorrow.

Image source, RHI Inquiry

He's already experienced a witness session in the Senate chamber, during the Northern Ireland Assembly's Public Accounts Committee hearings over the RHI debacle in October 2016.

Join us tomorrow from 09:45 for more live coverage, and have a great evening.

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DUP MP Ian Paisley lobbied an official to accept an RHI application for a more lucrative subsidy as rates were being cut, the inquiry heard.

Teri Clifton from Ofgem - the body that administered the initiative for DETI - said she took a "very intimidating" phonecall in November 2015.

Image source, Press Eye

She said she found she was speaking to the applicants, their representatives Action Renewables, Mr Paisley and the poultry producer Moy Park.

They all wanted her to accept the application after the deadline had passed because the applicants - the McNaughtons - otherwise stood to lose a considerable sum of money.

DETI contacted Ms Clifton about the McNaughtons' attempt to get on to the RHI scheme.

As a result, Ofgem carried out further checks to determine whether or not there had been an IT glitch that had halted the application - there hadn't been one.

Ultimately, responsibility lay with Action Renewables - the McNaughtons had handed their details to the group to submit the application on their behalf, but it hadn’t done it "at the point at which the applicants thought they had", explains Ms Clifton in her written statement.

Image source, RHI Inquiry

Ms Clifton believes Action Renewables' "lobbying" was therefore done in order to save its reputation.

The failure to get the application approved before the deadline "also had financial impact for the applicants, which was causing them a lot of upset", she adds.

The McNaughtons eventually got on to the RHI scheme but too late to receive the most lucrative subsidy rate.

After Ms Clifton dismissed the "lobbying" attempt to approve the McNaughtons' application under the most lucrative subsidy rate, Mr Paisley wrote to then DETI minster Jonathan Bell's adviser Timothy Cairns.

The MP wrote: "The gentleman has been in to see me along with the Ulster Farmers' Union and representative Teri Clifton in Ofgem, who are very concerned about the way his case has been handled."

Image source, Getty Images

Mr Aiken says Ms Clifton appears to have been presented in the letter as supporting the applicants' concerns about how their case had been handled by Ofgem.

"This isn't a fair representation of me endorsing that Ofgem were wrong at all," she tells the inquiry.

Sir Patrick says the letter reads like Ms Clifton had agreed that there was an IT failure at Ofgem that prevented the application from being received, but the witness replies: "There was no failure."

The DUP MP Ian Paisley was among a number of people who were "lobbying" Ms Clifton in a "very intimidating" phonecall to get her to approve an application to the RHI scheme under the most lucrative subsidy, even though the deadline had passed in late-2015.

In her written statement to the inquiry, she says that Mark Compston from Action Renewables "was unhappy" that she wouldn't allow the applicants to claim the higher rate because their form had been submitted too late.

Mr Compston claimed the deadline had been missed due to an IT problem at Ofgem's end, but Ms Clifton checked that and saw that it was not the case.

She later found herself on a call "without prior warning" with Mr Compston, Mr Paisley, the poultry producer Moy Park and the applicants - referred to as the McNaughtons - which she says "didn't feel appropriate".

"It was a really difficult situation, because you had lobbying going on on behalf of the applicants... and I just had to hold my ground."

There is a "very, very grey" about using a renewable heating system on the non-domestic RHI scheme to heat a house, explains Ms Clifton.

"We often have to ask the lawyers for an opinion around these cases," she says, explaining that some houses had been adapted to bring them under the eligibility criteria of the scheme.

Applicants had to provide rates bills to prove that the property that was being heated had a commercial purpose, and Ofgem would also make checks on invoices from the businesses concerned, as well as carrying out inspections before an application was approved.

"On the whole, we're trying to ascertain how much business is actually being done in that space," she Ms Clifton.

She reveals in her written witness statement that a Stormont department ran checks to see whether any ministerial advisers were benefiting from the scheme, after claims that one had been "inappropriately claiming" on the non-domestic initiative.

Ms Clifton says an investigation found that the unnamed adviser had been compliant with the rules.

In January last year, the Traditional Unionist Voice MLA Jim Allister used parliamentary privilege to allege that former DUP adviser Stephen Brimstone was using a non-domestic boiler to heat his home.

Back after the afternoon break, Mr Aiken apologies for returning to the subject of multiple boilers.

At the end of 2014, DETI official Seamus Hughes received a query from a man concerning the hypothetical installation of five boilers in one shed - it was discussed when Mr Hughes appeared before the inquiry this month.

As Mr Aiken puts it: "His common-sense reaction was that: 'You can't do that.'"

Nevertheless, Mr Hughes checked it out with Ofgem.

There was no official definition of a heating system in the regulations, so Ofgem determined that boilers that were separated hydraulically were to be regarded as individual heating systems, therefore being eligible for the more lucrative subsidy rate.

As Mr Aiken puts it, Mr Hughes' reaction was "that wasn't the policy intent - we didn't intend for somebody to be able to do this type of thing".

In her written evidence, Ms Clifton says "it wasn't Ofgem's role to find problems with the scheme".

She also describes the administrator's role as "a supportive operational adviser", adding that her assumption was that DETI was "monitoring and reviewing the scheme for trends".

In response to questioning from Mr Aiken, she says she would have reported anything relevant that had been communicated to Ofgem by the public.

"If I heard something, as I did on the helplines in 2015, where I had somebody say: 'Somebody has told me that this is happening', I felt that was my responsibility to tell DETI," she explains.

But she adds: "That's not monitoring - that's telling you what's going on on the ground."

Ofgem supplied DETI with weekly written reports, detailing facts and figures about the applicants to and claimants on the RHI scheme.

Looking at a spreadsheet that formed part of one of those reports, it's possible to observe the large numbers of the medium-sized biomass boilers that were eligible for a higher subsidy through the scheme.

It's not possible, however, to see the number of claimants who had installed multiple boilers, but Ms Clifton says you could work that out by noting the installations with sequential numbers that were commissioned on the same day.

Image source, RHI Inquiry

"Why not just have a column that says 'multiple boilers'?" asks inquiry panel member Dame Una O'Brien.

Ms Clifton says installations of multiple boilers were not necessarily a problem, adding a phrase we've heard many times from numerous witnesses: "I think hindsight's a great thing."

DETI eventually asked for more detail on claimants - names, addresses and postcodes - but it didn't ask for information on installations of multiple boilers installation.

When Ms Clifton joined Ofgem and started working on the RHI scheme for DETI, she noticed that the relationship with the department needed to be strengthened.

It had previously been "quite difficult, probably on both sides, from what I can gather".

Image source, Getty Images

During her time managing the running of the scheme for DETI, there was "a lot of engagement - it was mostly informal".

There were regular phonecalls, and Ofgem visited Belfast for the occasional meeting with DETI.

With the inquiry team off for a bite to eat, we'll do the same - see you back here at 14:00.

In Ofgem's fraud prevention strategy covering the RHI schemes in both Great Britain and Northern Ireland, it is recognised that the design of the two initiatives "may allow opportunity for gaming".

Gaming was the practice of installation of multiple small boilers that were eligible for a higher subsidy instead of one larger, more efficient unit that was subject to a lower subsidy - that allowed claimants to collect more money.

The document notes that gaming is "not fraud as [it is] not in breach of the regulations", although it might be in breach of the spirit of the scheme.

It goes on to say that if Ofgem detected any gaming it would report it so that DECC - which was running the GB scheme - would be aware of it, in case it wanted to close the loophole with a change to the legislation behind the scheme.

But there's no mention of DETI, so would Ofgem have informed the Stormont department if the same issue arose?

Ms Clifton says it's a simple, unintended omission, and DETI had always been "at the forefront of my mind", adding: "They aren't seen as any less important [than DECC]."

Mr Aiken asks if the counter-fraud strategy was effectively the opposite of an anti-fraud strategy.

"What does that say about the level of understanding, attention that was being paid to Northern Ireland RHI scheme?"

There's a long pause before Ms Clifton replies: "I can see the point."

Mr Aiken says the document was supplied to senior management in Ofgem, so why did no-one spot the fundamental error?

Ms Clifton says the only defence she can offer is that at this point the Northern Ireland RHI was "a very low take-up scheme".

The RHI schemes in Great Britain and Northern Ireland were both covered by the same fraud prevention strategy.

Mr Aiken displays an edition from December 2013, which lists the measures in place to prevent the generation of unnecessary heat purely in order to claim RHI payments.

Image source, RHI Inquiry

One of those is measures is "the tiered tariff for biomass".

"As far as the NI scheme was concerned, that's just wrong," says Mr Aiken.

"Yes it is - because there was no tiering," Ms Clifton replies.

In the first five months of 2015, there were about 50 applications a month to the RHI scheme, says Ms Clifton, giving no "cause for concern".

Image source, Reuters

"Suddenly", she says, the number spiked.

Mr Aiken compares it to "Mount Etna - this is a volcano".

Two years' worth of applications to the RHI scheme were received in just two months in autumn 2015, an internal Ofgem document shows.

That spike in applications caused the catastrophic bursting of the initiative's budget, eventually leading to its vast overspend of hundreds of millions of pounds, with DETI scrambling to close the scheme shortly afterwards.

Image source, Getty Images

Asked how Ofgem managed to deal with that "tsunami" of applications, Ms Clifton explains: "It was an interesting job - it was extremely busy on all fronts."

In October that year, there were 179 application to the GB RHI scheme.

The Northern Ireland scheme, which should - in theory - have had about 3% of the number of applications made to the GB initiative, actually received a total of 504.

Mr Aiken displays an Ofgem "difficult decisions table" from the summer of 2013, which was supplied to Ofgem's management committee

It refers to an article in the agricultural news publication Farmers Weekly about a poultry farm site, which the Ofgem document says "is arguably, but not conclusively, installing separate heating networks to be able to maximise RHI revenues by exploiting the tiered tariff concept".

Image source, PA

"We have estimated the total payment over 20 years for 14 accredited installations at the site in Farmers Weekly to be £11.6m," it continues.

The document says that the Department of Energy and Climate Change (DECC) - the government department that ran the GB RHI scheme - had been informed.

Mr Aiken says there's no evidence that the information was ever supplied to DETI, which operated the Northern Ireland initiative.

Ofgem's reports show that a "high proportion of non-compliance" with the rules of the RHI scheme by claimants was being discovered, says Mr Aiken, giving a figure of 46%.

Image source, Getty Images

Ms Clifton says much of that was down to poor record-keeping by claimants - it wasn't considered to be a serious issue and could be easily fixed.

But more serious issues could be examined in a fraud investigation.

Some biomass boiler installers in Northern Ireland were "frequent" callers to the RHI scheme's administration team, according to Ms Clifton.

Image source, Getty Images

They were asking for information about the scheme, she explains, but staff were trained to tell them that any "speculative queries" should be diverted to DETI.

"If something came left-field and we weren't sure... if it wasn't to do with administration we would refer them back to DETI."

Ofgem's administration operation for the RHI scheme was split between London and Glasgow - London mainly dealt with the technical and legal aspects, while the operational side was situated north of the border.

The operational team provided a weekly report on the RHI scheme.

Ms Clifton explains that a section on "periodic data" included meter readings of biomass boilers sent in by scheme participants, and those would be checked by Ofgem staff against readings from previous months to identify any irregularities.

Image source, Getty Images

"It's not just a fraud indicator - what you could be seeing is people's meters not reading properly," she says.

"But also it could be an early indicator that we're not quite happy with something and it might need further investigation."

The information contained in the reports is extensive and detailed, but it was not shared with DETI, and Mr Aiken asks if there was any reason why it couldn't have been shared.

"I don't think so," says Ms Clifton, adding that it wasn't being shared when she started working on the scheme.