The sun has long since disappeared behind the Belfast hills as we reach the end of another heavy-duty day up at Stormont.

Hard to believe it, but having just endured a five-hour grilling from the PAC, Dr Andrew McCormick is back up at Parliament Buildings tomorrow afternoon to appear before the assembly's Economy Committee... and we'll be across it, of course.

Image source, Getty Images

MLAs will also hear from the Renewable Heat Association, a group of boiler operators who have pledged to defend their interests in court if the economy minister attempts any rescue plan they believe goes against their interests.

Join us tomorrow at 10:00 or be out of the loop...

Goodnight!

In final chapter of this gruelling session, Sinn Féin's Oliver McMullan asks if any of the boiler installation firms connected to the RHI scheme were related to "any of the [advisers] within the DUP".

The DUP's Trevor Clarke intervenes: "Why only the DUP? What about about Sinn Féin, Ulster Unionist Party, SDLP and Alliance?

"Just shows it is a witch-hunt."

On the matter of the list of installers, Mr McMullan says: "I would like to get it before Nolan gets it!"

Sinn Féin's Michelle Gildernew points out that DUP aide Andrew Crawford has responded to the Dr Andrew McCormick's belief earlier in today's inquiry session that he applied pressure over the running of the scheme.

Speaking from her experience as a minister in the executive, Ms Gildernew adds: "The buck stops with the minister, regardless of what department it is."

An executive minister is responsible for the actions of his or her adviser, even if those are unauthorised, Dr Andrew McCormick confirms under questioning from Trevor Lunn.

The Alliance Party MLA says "ministerial responsibility extends to the actions of her spad, whether or not they've authorised that action".

"His or her," Dr McCormick adds.

Back to Jonathan Bell's interview with the BBC's Stephen Nolan, and DUP MLA Trevor Clarke presses Dr Andrew McCormick on the validity of some of the claims.

The civil servant says that when he was watching the interview there was an "important stage when there was something very clearly misleading" in relation to a conversation that happened between him and Mr Bell.

It was "very unclear indeed on the timing and sequence of events".

On another of Mr Bell's claims that advisers asked for references to Arlene Foster to be removed from executive documents relating to the RHI scheme, Dr McCormick says that he says there is no evidence to prove that.

With Mr Bell sitting just behind him, he says there was a change to a document but it was of "no consequence whatsoever".

It's been a tense, marathon PAC inquiry session, but now a light-hearted moment...

DUP MLA Carla Lockhart provokes laughter when she says Dr Andrew McCormick is "one of the longest-serving permanent secretaries... at the minute".

"You're pre-judging something there," committee chair Robin Swann jokes.

But Ms Lockhart quickly recovers and says: "I'm saying you're very long in the tooth - you're experienced!"

"You're experienced compared to us young whippersnappers."

Quizzing Dr Andrew McCormick on the Department for the Economy's plan to mitigate the scheme's proposed £490m additional cost to the taxpayer, Sinn Féin's Declan Kearney asks if it will only work if the inspection of installations is "robust and effective".

The permanent secretary says the proposed legislation would effectively be a "tourniquet" that will stop the flow of public money through the initiative.

Staying on the medical theme, he adds that a "surgeon" is needed to "cut off the things that are wrong" with the scheme.

He says there is "great confidence that we can do well" in terms of clawing back the near half-a-billion pounds that has been committed through the scheme over the next 20 years.

The EU needs to approve the regulations, but Dr McCormick says he is hopeful that that will happen "quickly".

Outside the Senate chamber, DUP adviser Andrew Crawford has responded to the belief Dr Andrew McCormick expressed earlier that he had exerted influence over the running of the RHI scheme.

The aide says he spoke to then DETI adviser Timothy Cairns in summer 2015 about the initiative, but those discussions "would have been on the basis of my experience of the department".

He says he would have been "offering informal advice and assistance as a colleague" to his successor in the and "not on behalf of the finance minister or the party".

"However, as I pointed out to the BBC in December, I did not attempt to keep the RHI scheme open at the original tariff against the wishes of the minister," Mr Crawford adds.

"Indeed, I specifically stated on 31 July 2015 that the department 'will need to make changes from 1 October.'"

Inquiry chair Robin Swann asks Dr Andrew McCormick about meetings with poultry producer Moy Park and County Fermanagh-based wood pellet manufacturer Balcas.

He explains that it is quite usual for officials to meet "substantial stakeholders" and that it is part of their job.

In reply to a question from Sinn Féin's Oliver McMullan, the official explains that the pellet boilers are "a very good form of heat" for poultry.

"The success of the poultry sector has been enhanced by access to the scheme," he says.

The committee gets in to allegations made by DUP MLA and former enterprise minister Jonathan Bell in an interview with the BBC's Stephen Nolan last month.

When the DUP's Gordon Dunne asks whether all of those claims were accurate, Dr Andrew McCormick says: "No."

Image source, PA

He goes on to say that delay in addressing the RHI scheme as applications began to spike in autumn 2015 was "affected" by the DUP's "resignations and reappointment" of ministers under the party leader Peter Robinson's (above) direction during what was Stormont's last political crisis before the current one...

Doesn't that seem like a quite a while ago...?

Sinn Féin's Declan Kearney asks Dr Andrew McCormick whether he has been prevented from speaking to the media by the economy minister.

The BBC has asked the Department for the Economy on more than one occasion for an interview with the permanent secretary.

Dr McCormick says there have been "several discussions" on the matter and the judgement was that he would instead give "primacy" to answering to the PAC.

He says that is his "responsibility".

Attention turns to the "whistleblower", known as the concerned citizen who first raised concerns about the RHI scheme.

Dr Andrew McCormick says her email to Arlene Foster's personal email address was never passed on to civil servants at the then Department for Enterprise, Trade and Investment (Deti).

Dr McCormick  tells the committee the whistleblower was "unhappy with the way" concerns she raised to the department were handled, and he adds that "we have to accept our role in relation to that".

"What I can says is that the meeting with officials happened as recorded, and she was not believed, and that's, to me, a big cause for concern," he adds.

After a short comfort break, the PAC members, witnesses and those in the public gallery in the Senate chamber take their seats again and settle in for what could be another lengthy session.

Ulster Unionist Robbie Butler asks the Department for the Economy (DfE) officials about the 19 installations of RHI scheme boilers identified by investigators from the professional services firm PwC as being in the most serious category.

Image source, Thinkstock

"These were installations which were predominantly for domestic heating, or were creating heat solely for the purpose of collecting the RHI grant," he says.

DfE official Brendan McCann says 13 of those have had payments suspended, "and they are being investigated by [scheme administrators] Ofgem".

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Stormont's enterprise department faced "political pressure" over the RHI scheme in 2015, Dr Andrew McCormick says with hindsight, but it did not "feel like a sinister pressure".

That was because civil servants were not aware of the flaws with the scheme at that time.

He says the civil service views advisers as an extension of the minister they serve and "always makes the assumption" that the aides are acting on their behalf.

But he goes on to say that he is not suggesting "the influence from Andrew Crawford" was as a result of "instigation" from then finance minister Arlene Foster.

"I haven't heard anybody say that - that's not even hearsay," he adds.

Oliver McMullan brings Dr Andrew McCormick right back to the original business case for the scheme.

"Built into that business case were regular reviews," he says, and he asks how many reviews there had been between 2012 to 2015.

Image source, Tchara

"There weren't any," comes the reply.

"That's the problem, I agree," says Dr McCormick.

DUP adviser Andrew Crawford has more "knowledge of the scheme and its failings" than most people, Sinn Féin's Michelle Gildernew says.

That, she says, is because he has been an adviser to several executive ministers over the past few years.

"It seems to me unbelievable that there wouldn't have been conversations between him and the firs minister even before January [2015]," she says.

"There seems to be a common denominator throughout."

Dr Andrew McCormick again says he has no evidence on that point but he understands "the inference you'e making".

Mr Crawford was named by Dr McCormick earlier as the person he believed was exerting influence to prevent cost controls being added to the scheme in 2015.

Internal investigations into the RHI scheme cannot delve into issues relating to ministerial advisers, Dr Andrew McCormick says.

When Sinn Féin MLA Michelle Gildernew asks him if he has any knowledge of conflicts-of-interest in the scheme around DUP advisers, as former enterprise minister Jonathan Bell alleged in the assembly yesterday.

The Department for the Economy permanent secretary says those matters can only be dealt with by a wider inquiry.

The advisers named by Mr Bell under parliamentary privilege have denied his claims, with the DUP saying his remarks were "outrageous".

Arlene Foster's letter when she was enterprise minister to banks encouraging them to support applicants to the RHI scheme was "totally reasonable", Dr Andrew McCormick says.

He says at the time there was no evidence that anyone was "aware of any flaws" in the initiative.

Committee chair Robin Swann asks would it be normal practice for such correspondence to be sent.

Dr McCormick says that drawing attention to it was "perfectly normal, reasonable thing to do" to advertise it and encourage uptake at a time when demand for the scheme was low.

Arlene Foster acted on the advice of "educated" and "well-read" civil servants, the DUP's Carla Lockhart says.

She asks Dr Andrew McCormick to clarify that that was indeed the case, and he reiterates his point that she followed advice from official when she was enterprise minister.

He tells the committee that "ministers have the right to expect civil servants will get this kind of thing right".