It's been a long day in the Senate chamber - the inquiry has run about 25 minutes over its usual finishing time - and there's much more to come from Mr Cairns tomorrow morning.

The inquiry barrister Donal Lunny says he's rightly on track with getting through the long list of questions for the witness.

We'll be back at Stormont from 09:45 tomorrow to hear what has to be said so please do join us then.

For now, though, it's good evening from us!

Jayne McCormack
BBC News NI politics reporter

A former DUP adviser admitted that he was prepared to go along with the party's narrative about the RHI debacle when details of the flawed energy scheme emerged in December 2016.

Tim Cairns was giving evidence to the RHI Inquiry for the first time.

Image source, Pacemaker

Last week, former minister Jonathan Bell claimed he had been the victim of a "smear campaign" by the DUP when he spoke out about problems with the RHI.

Mr Cairns, who was Mr Bell's adviser, told the inquiry that politics was a "grubby world" but denied that his involvement amounted to the smear campaign that his former minister had suggested.

Mr Cairns insists that Mr Bell did not read submissions that were provided to him by DETI civil servants.

He claims in his written evidence that the minister "boasted" that he would've just read the cover page and ignored the rest.

Mr Johnston says in his evidence that Mr Bell has a "lack of focus" when it came to reading documents.

Image source, RHI Inquiry

He also claims that he told the then first first minister Peter Robinson that Mr Bell was "not a suitable candidate" for the post of enterprise minister.

The minister's private secretary Sean Kerr says that his experience was that the minister read papers in a "summary" fashion.

In Mr Bell's evidence, he says he read ministerial papers from cover to cover and "often read them into the early hours of the morning and my wife can attest to that".

With the RHI scheme's budget badly running out of control in the summer of 2015, civil servants at DETI were working on ways to rein it in and outlined their plan in a submission that was written for Mr Bell on 8 July.

Mr Cairns had been told at in the second week of June that the plan was urgent but it took a full month for it to be put into writing for the minister.

Image source, Getty Images

It stated that the expected spend on the scheme would exceed the budget set aside for it and attributed that to a large number of poultry farmers signing up.

Mr Bell told the inquiry last week that there's no evidence of him receiving or signing the document.

Mr Cairns says he can't remember giving Mr Bell a copy of the paper but he told him about it twice in July and on the first occasion - the day after it was published - he sat beside him, taking him through the detail.

The RHI scheme was discussed at the clear-the-air meeting, says Mr Cairns, and Mr Johnston had - in the presence of Mr Bell - asked him to talk to Arlene Foster's adviser Dr Andrew Crawford about it.

He says in his statement to the inquiry that it was at that meeting that Mr Johnston said cost controls for the RHI would not be introduced.

Image source, RHI Inquiry

Mr Johnston's evidence about the meeting is very different - he insists that that the energy scheme was not specifically discussed.

Inquiry chair Sir Patrick Coghlin asks Mr Cairns how sure he is that the senior DUP adviser told him that the subsidies on offer from the scheme would not be cut.

The witness says he believes Mr Johnston did say it, adding: "That's my recollection - I'm not going to go to the sword on it."

Mr Bell claimed last week that he and his adviser had "socialised together [and] enjoyed ourselves" in the weeks and months after their clear-the-air meeting - their families had even "built sandcastles" on Portstewart beach!

But Mr Cairns says he can "state categorically" that there was "no socialising" after their row and Mr Bell's account was "vastly in excess of what I can remember".

Image source, Getty Images

He says Mr Bell's suggestions that they watched football together is "pie in the sky".

Instead, after their row in June 2015 the relationship became "professional only".

Mr Cairns claims that Mr Johnston (below) had assured him that Mr Bell would make an apology at the clear-the-air meeting, allowing for their working relationship to be restored.

But when the meeting took place the minister refused to apologise and said he had done nothing wrong.

Image source, Press Eye

Mr Cairns says the assurance he'd been given by Mr Johnston the night before about mutual apologies had been "worthless".

He says he agreed to return to his role but he believes now that it was the wrong decision.

The day after the meeting he complained in a text message to Mr Johnston, saying that "in my view [Mr Bell] has got away with it again - I do not feel yesterday was fair".

Former DUP leader Peter Robinson was "not giving enough weight or taking seriously" allegations about Mr Bell's behaviour in London, says Mr Cairns.

That caused the adviser "stress heaped upon stress" and he was subsequently signed off work by a doctor.

He claims he was invited by Mr Johnston to a clear-the-air meeting with Mr Bell and says that during a phonecall about it Mr Johnston gave him two options - reconcile with the minister or lose his job.

Image source, RHI Inquiry

He tells the inquiry that the situation was "exceptionally upsetting" and is "still upsetting to talk about".

Asked if he thought about not going back to his adviser role, he replies: "I guess we've got mortgages to pay and bills to pay and... life."

After discussing it with his wife he decided that going back would be "purgatory" but with a Northern Ireland Assembly election on the horizon the next spring "this too shall pass".

Mr Cairns says that when he returned to Belfast after the London incidents he fully expected to be removed as Mr Bell's adviser and that he'd be moved to work for another minister or to a role in the DUP.

Image source, RHI Inquiry

Inquiry barrister Mr Lunny (above) presses the witness a number of times about whether the reason he remained in his post was because the minister concerned was Mr Bell.

"That's probably a fair assertion," he says, adding that senior DUP adviser Timothy Johnston phoned Mr Bell to tell the minister that Mr Cairns would not be sacked.

On his return to the breakfast table a short time later, Mr Bell's anger had "ratcheted up" and he told his adviser that he would be fired if he left again, according to Mr Cairns.

He says he "must've been" wagging a finger at Mr Bell, who he then claims made a "physical grab" for it.

Image source, Getty Images

"He said: 'If you wag your finger at me again I'll break it'," says Mr Cairns.

"He was standing up at that point, people were looking around - I just wanted out of the room."

He says that Mr Bell demanded an apology from his adviser but when he refused to give one the minister told him he was fired.

A row over breakfast the morning after the Indian restaurant discussion was "not the proudest moment of my working career", admits Mr Cairns, who admits he made "many mistakes" during it.

His "frustration boiled over inappropriately" and there was a "sharp exchange" between him and Mr Bell.

Image source, RHI Inquiry

He says he was trying to advise that a decision that DETI was attempting to proceed with on an energy scheme unrelated to the RHI had no support from MLAs would be difficult to pass.

Mr Bell gave his account of the row last week, saying that he believed Mr Cairns had been challenging "my ability to function as a minister".

"This could all have been handled better," acknowledges Mr Cairns, who says he left the table.

On a trip to London on 9 June 2015, Mr Cairns and Mr Bell went for dinner in an Indian restaurant, durig which the adviser put it to the minister that they could meet Arlene Foster and her adviser to discuss DETI matters as they had considerable experience in the department.

"Mr Bell was very much of the opinion that these issues would be under his control and there wouldn't be any input from minister Foster or Dr Crawford," says the witness.

Image source, Getty Images

He says he closed the conversation down when Mr Bell became "somewhat heated" as he didn't want it to become "unsavoury".

Giving the inquiry his interpretation of his minister's concerns, he says that it was "fairly clear that minister Foster had been exceptionally popular inside DETI and outside DETI" and that Mr Bell was "feeling that".

Image source, RHI Inquiry

Ready for action again, Tim Cairns settles into the witness chair in the Senate chamber.

Inquiry barrister Donal Lunny begins asking questions about an incident Jonathan Bell and Mr Cairns had in a London curry house in the summer of 2015.

Jayne McCormack
BBC News NI politics reporter

A former DUP adviser admitted that he was prepared to go along with the party's narrative about the RHI debacle when details of the flawed energy scheme emerged in December 2016.

Tim Cairns (below, left) is giving his first day of evidence to the RHI Inquiry.

Last week, former minister Jonathan Bell (above, right) claimed he had been the victim of a "smear campaign" by the DUP when he spoke out about problems with the RHI.

Mr Cairns, who was Mr Bell's adviser, told the inquiry that politics was a "grubby world" but denied that his involvement amounted to the smear campaign that his former minister had suggested.

A busy opening session of the week and there'l be much more to come after Mr Cairns and the inquiry team have a beak for a bite to eat.

The Q&A resumes at 14:00 - join us again then.

Arlene Foster and her adviser Dr Andrew Crawford claimed they knew nothing about problems with the RHI scheme during a meeting on 8 June 2015, says Mr Cairns.

He claims he met them briefly straight after the meeting he'd been involved in with the DETI minister and his officials on the same day, during which civil servants said the initiative was facing budget issues.

Image source, PA

Both Mrs Foster and her adviser had moved from the department running the scheme to the finance department a few weeks earlier.

Mr Cairns tells the inquiry: "They said: 'This is the firs we've heard about that', and I said: 'I'll keep you updated'."

Mrs Foster says in her evidence that the meeting happened at the end of June, while Dr Crawford can't remember it - Mr Cairns is adamant that it happened on 8 June.

Mr Cairns says he believes he first became aware that RHI was over budget at a meeting on 8 June 2015 attended by himself, the enterprise minister Mr Bell and senior DETI officials.

Image source, RHI Inquiry

DETI's deputy permanent secretary Chris Stewart emailed a colleague after the meeting, stating that Mr Bell had asked to be kept informed about a number of issues about the RHI, including legislation on changes to the subsidies it offered.

Asked if he can remember the minister's contribution to the meeting Mr Cairns says: "Jonathan would have sat quite passively while these discussions were happening."

Mr Cairns says he can only give a "flat denial" of the suggestion that he tried to keep the RHI scheme off the agenda in meetings involving the enterprise minister and officials in May and June 2015.

"No discussion was shut down at any time with anybody by me," he insists.

Image source, Getty Images

The claim was made by Mr Bell in his evidence to the inquiry.

The DETI permanent secretary Dr Andrew McCormick told the inquiry last week that he didn't "recall any resistance" from Mr Cairns to having the scheme discussed in meetings.

Mr Cairns denies that he'd told Mr Bell that he couldn't cut the subsidies offered by the RHI scheme because DUP advisers had interests in the poultry industry.

Mr Bell claimed that it was one of the first pieces of advice his adviser had given to him when they began working at DETI.

Image source, Getty Images

He claimed Mr Cairns told him that Mr Johnston and John Robinson had "extensive interests" in the poultry industry and therefore the scheme couldn't be changed.

Mr Cairns says he knew nothing about the energy initiative when he arrived at DETI and so finds it hard to know "how, why and when" he would have said it.

Timothy Johnston is "at the top of the tree with the Democratic Unionist Party" and his influence was felt from "top to bottom", says Mr Cairns.

And there was "not one elected representative, not one party employee or special adviser who did not recognise that", he adds.

Mr Johnston, now the party's chief executive, says in his evidence that there was no hierarchy of advisers.

Mr Cairns claims in his witness statement that Mr Johnston, "in running party matters while [an adviser], was operating outside of what he was permitted to do".

He also says that it would "obviously be problematic for the DUP if the media were to get hold of the story".

Mr Johnston's influence within the DUP was seen from "top to bottom", claims Mr Cairns, and his responsibilities even included staff reviews and chairing weekly party meetings.