It's not been an easy time at the inquiry for Trevor Cooper - the chair Sir Patrick Coghlin says he's been subjected to "persistent and aimed questioning".

"I am quite sure... it has not been a particularly pleasant and comfortable exercise for you," he tells the witness before thanking him for the substantial amount of evidence he's provided.

Image source, Reuters

Tomorrow the inquiry will hear from Northern Ireland's comptroller and auditor general Kieran Donnelly and Department for the Economy official Michael Woods.

Join us at the usual time of 09:45 for more live coverage - have a great evening!

BBC News NI

Stormont civil servants failed to make sure that adequate checks were done to guarantee spending controls were in place in the RHI scheme, the inquiry heard.

Image source, Getty

An internal scrutiny panel signed off the RHI in 2011 after taking a colleague's word that spending could be stopped if the initiative went beyond its budget.

But that assurance was not correct and inquiry chair Sir Patrick Coghlin said the civil servants who sat on the scrutiny panel would have found that out for themselves if they had read the scheme's rules.

Stormont civil servants running schemes and projects see proper governance processes as "unnecessary", "too bureaucratic" and "just [getting] in the way of delivery", according to Trevor Cooper.

"I would say that's part of the culture across the civil service," he adds.

Image source, Getty Images

He makes the remarks after Dame Una O'Brien says it's important that financial officials in departments have the "authority, respect and clout" that they need to have to ensure that public money is spent properly.

Trevor Cooper says he doesn't believe that was the case in DETI.

He believes civil servants working on policy need to understand why finance officials insist on things being done in the proper way and that those conditions are not optional.

There are multiple examples of documents that DETI officials changed in order "put fig leaves" over the problems of the RHI scheme, says Dr Keith MacLean.

Image source, Getty Images

The inquiry panellist's view is that "everybody seems to be as complicit in this as everybody else" in changing papers "to say what they want it to say" whether or not that was accurate, misleading or otherwise.

"It's hard to take any document at face value," he says, adding that it didn't create a "clear picture" about what was happening for decision makers such as the DETI minister.

A key warning about the spending on the RHI scheme was removed from a document that was prepared for the enterprise minister Jonathan Bell in July 2015.

Officials knew that there would be consequences for the department's own budget if there was an overspend.

Image source, PA

But the final paper that was given to the minister didn't mention that and the inquiry hears that Trevor Cooper raised concerns with his boss Eugene Rooney that the warning was taken out.

The then DETI permanent secretary Dr Andrew McCormick told the inquiry last week the submission Mr Bell received was "inaccurate and misleading".

Visibly frustrated, Mr Cooper says he didn't feel his boss listened to his concern and he would've liked the content of the paper "to have been put back to the original".

A lack of written records hindered civil servants' ability to sort out the problems with the RHI scheme in June 2015, accepts Trevor Cooper.

Image source, RHI Inquiry

Dame Una O'Brien tells him that he and other officials who were dealing with the RHI didn't have "any framework" to guide them in solving the issues they were facing.

"Absolutely, I totally agree," replies the witness as he shakes his head and looks to the Senate chamber ceiling.

DETI civil servants were given legal advice that cutting subsidies was the only control mechanism for the RHI scheme that could be implemented quickly, claims Trevor Cooper.

He says energy team officials Stuart Wightman and John Mills told fellow civil servants at a meeting on 17 June 2015 that they had obtained verbal advice to that effect.

Sir Patrick Coghlin wants to establish whether that advice actually existed: "It is quite important if there was legal advice - if there was... I would certainly like to know who gave it."

After a bit of digging during a break in proceedings, Joseph Aiken finds something that shows a civil service solicitor said he "doesn't favour the suspension route" given that prospective applicants could've spent big money on new heating systems only to see the RHI pulled from under them before they signed up, leaving them massively out of pocket.

Mr Aiken says it "doesn't appear to sit easily" with Mr Cooper's recollection of events, which the witness accepts.

There was a "complete lack of understanding" among DETI officials about what needed to be done to get the RHI scheme under control, says Sir Patrick Coghlin.

Image source, RHI Inquiry

There was a "failure" to check how legal powers come be used to suspend the scheme.

Trevor Cooper says the inquiry chair's comments are fair and he accepts there was a misunderstanding about what could and couldn't be done.

In trying to get the RHI scheme under some control, officials pursed a proposal to reduce the subsidies paid to claimants after they'd used their heating system for a certain amount of hours in a year.

Another possible option was a legal power to suspend the scheme at any time but Trevor Cooper says his understanding was the emergency stop button would've taken too long to be approved.

Officials believed it had to be put to the public in a consultation lasting several weeks.

Image source, Getty Images

They thought subsidy cuts could be implemented quickly because DETI had put a broad proposal of cost controls to public consultation in 2013.

But what had been put to the public in the past was different to the cost control mechanism the department was intending to add in autumn 2015.

Inquiry chair Sir Patrick Coghlin asks what the difference was in time taken to implement the two possibilities, given that they both required legislation.

Mr Cooper doesn't know why he was told the alternatives to subsidy reduction would take too long and says: "Maybe I picked it up wrong."

Trevor Cooper had a hand in working on the business case for the addition of cost controls to the RHI scheme in 2015, even though he would ultimately chair a panel of senior officials that was supposed to provide an independent scrutiny of it.

The paper was drawn up by the team working directly on the RHI but it was shared with and had input from DETI finance officials including Mr Cooper and Shane Murphy, a departmental economist.

The inquiry barrister Joseph Aiken says the evidence suggests they had a "substantive" involvement in its content and did more than "adding full stops and commas".

That's a potential problem because the two men would later assess and approve it before it was sent to Stormont's finance department for a final rubber stamp.

Mr Cooper says his involvement was only to the extent of making sure the business case had the necessary detail the finance department would require.

But Dame Una O'Brien says it's clear he'd been involved "quite extensively" and asks whether it was ever suggested he therefore shouldn't chair the independent scrutiny panel.

Mr Cooper says that was never suggested.

The final public hearings of the RHI Inquiry will take place next week and it's fair to say it's going out with a bang.

Former finance Máirtín Ó Muilleoir will be the first and only Sinn Féin figure to give oral evidence - he set up the inquiry back in January 2017.

He's likely to be asked, among other things, about an email he sent in February 2017 in which he said his party would "do our utmost" to get as many applicants as possible "green-lighted", external before the RHI was shut down that month.

Image source, RHI Inquiry

The inquiry will also hear from the DUP's Simon Hamilton, a former economy minister who was responsible for the dealing with the RHI after it closed.

And the former and current heads of the Northern Ireland Civil Service - Sir Malcolm McKibbin and David Sterling - will get a say at the back end of the week.

You can watch and follow every minute of it with us here at BBC News NI.

BBC News NI

Stormont civil servants failed to make sure that adequate checks were done to guarantee spending controls were in place in the RHI scheme, the inquiry heard.

Image source, Pacemaker

An internal scrutiny panel signed off the RHI in 2011 after taking a colleague's word that spending could be stopped if the initiative went beyond its budget.

But that assurance was not correct and inquiry chair Sir Patrick Coghlin said the civil servants who sat on the scrutiny panel would have found that out for themselves if they had read the scheme's rules.

Image source, RHI Inquiry

Inquiry barrister Joseph Aiken raises smiles all round the Senate chamber when he promises to finish his questioning of Trevor Cooper bang on time at 16:45.

Sir Patrick Coghlin is holding him to that!

The final furlong is in sight for Trevor Cooper - join us again after the break from 14:00.

Trevor Cooper admits he didn't pick up the reference in the RHI scheme's business case about to how the initiative was being exploited.

Sir Patrick Coghlin wants to know why it wasn't noticed, saying that he can't see why it "didn't just jump off the page".

Image source, RHI Inquiry

"It's a scheme that was running well above budget, it was producing 33% returns," he adds, suggesting that even the "man or woman on the street" would've been asking questions about what was going on if they'd seen the reference.

Mr Cooper is told by Joseph Aiken that the inquiry panel may "struggle" with the fact that civil servants didn't feel they needed to reassess what was happening with the RHI.

Inquiry counsel Joseph Aiken introduces the draft of the business case produced by Stuart Wightman on 27 July 2015 for the RHI scheme changes.

It includes DETI's first written referral to participants gaming the scheme - that was a way of exploiting it to collect more subsidies.

Mr Wightman wrote that cuts to subsidies would reduce the risk of gaming and installations being operated over and above" a claimant's required heat need "just to generate RHI income.

Trevor Cooper agrees that reading that should've set off an alarm with him but it didn't.

It's put to him that by the end of July that year everyone in DETI involved with the RHI knew there was a risk that the scheme was facilitating people to operate their boilers solely to generate income.

"No, there absolutely wasn't," he replies.

One of Trevor Cooper's "greatest regrets" in the RHI fiasco is "not putting hell of a lot more down in writing".

He says there was a lot of verbal communication - he claims he told his boss about the issues he had with the inaccurate RHI paper that energy officials had sent to him in June 2015.

Image source, Getty Images

"You're just so busy... you're moving from one fire to the next with absolutely no pause for thought."

But inquiry panellist Dr Keith MacLean says that passing information on to bosses is "not the same as getting the sleeves rolled up and sorting out what the problem actually was".

Shaking his head, Mr Cooper doesn't think he can be "criticised for not rolling my sleeves up in this" because he flagged up problems with people who were best placed to deal with them.

The team working directly on the RHI scheme drew up a paper on the RHI scheme in June 2015 that contained multiple inaccuracies, painting a much rosier picture of the finances.

Parts of the document would ultimately go to the finance department but it was sent to Trevor Cooper that month.

He sent it to a colleague, noting that it contained a "fair bit of naivete", lacked a factual basis for some of its claims and there was "no self-awareness" on the part of the author Stuart Wightman that the RHI might be overcompensating its claimants.

Image source, RHI Inquiry

Inquiry counsel Joseph Aiken asks why Mr Cooper didn't say to Mr Wightman that there was "no point in dressing this up as something it isn't... it's going to come back to haunt us all".

Dame Una O'Brien wants to know why he didn't get the RHI team around a table to talk them through the problems with their document.

Sir Patrick Coghlin says there was an onus on Mr Cooper as the head of finance to "correct the record".

A "fig leaf" was raised to cover the fact that DETI hadn't carried out a review of the RHI scheme, as it had been required to do, claims Trevor Cooper.

He says Stuart Wightman (below), the man who was managing the RHI, told senior department officials about the failure to do a review at a meeting at the start of June 2015.

Image source, RHI Inquiry

The officials then wondered whether they could present information to the finance department that would suggest something had been done, says Mr Cooper.

"There was no agreement to it but there was no demurring, let's put it like that," adds the civil servant.

There's is no defence for why DETI civil servants provided inaccurate information about the RHI scheme to Stormont's finance department, admits Trevor Cooper.

Joseph Aiken wants to know what was going on in DETI that led to that appearing to be acceptable - he wonders whether a "laziness" or a "casualness, or a carelessness" had crept into civil servants' work.

"Is that just a human mistake or is that a cultural thing?" he asks.

Mr Cooper says it's "potentially cultural".