Officials at DETI draw up a submission for their minister Mr Bell on 8 July - it outlined their plans for adding cost controls to the RHI scheme that would help to cut the vast overspend it was facing.

Mr Cairns told the inquiry yesterday that he talked Mr Bell through the details of the paper but the former minister has said there's no evidence that he ever received it.

Image source, Getty Images

On 16 July, Mr Cairns shared the submission with his fellow DUP advisers Dr Andrew Crawford and Stephen Brimstone for their "information and input".

He tells the inquiry he had done that on the instruction of senior DUP adviser Timothy Johnston, who advised him to talk to Dr Crawford about the changes to the scheme.

Mr Cairns says there was "no secret" that he was seeking advice on the planned changes to the RHI scheme from other party advisers.

Tim Cairns (below, left) was Jonathan Bell's adviser at Stormont's Department of Enterprise, Trade and Investment (DETI) in 2015 and 2016 and offered guidance to the minister about the controversial RHI scheme.

His version of the RHI debacle is almost completely opposing to that of Mr Bell (below, right).

He has a colourful and varied background - he worked as a solicitor before going to Canada to study religion and he became a pastor for three years.

On his return to Northern Ireland in 2011 he worked for the DUP as its head of policy before advising Mr Bell when he was a junior minister at Stormont.

He also ran Gavin Robinson's Westminster election campaign in 2015, after which he began working with Mr Bell at DETI.

His time as a DUP adviser ended in May 2016 and he now works as the Northern Ireland director for the Community Transport Association, a transport services charity.

Back in the witness chair for a second day of evidence to the inquiry, Tim Cairns sits with his hands clasped.

This morning's questioning is going to be focused on the summer of 2015, primarily the roles of Mr Cairns, other DUP advisers and the enterprise minister Jonathan Bell when civil servants were trying to rein in the spending on the RHI scheme.

Image source, RHI Inquiry

If you want to quickly catch-up on what happened yesterday, check out our coverage.

Mr Cairns has given three witness statements to the inquiry and they're brimming with intriguing details - you can find them here, external, here, external and here, external.

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

Jayne McCormack
BBC News NI politics reporter

Two former DUP advisers have disputed events at a meeting in which it was claimed one told the other that cost controls would not be introduced to the RHI scheme, the inquiry heard.

Tim Cairns alleged that Timothy Johnston (above) made the comment during a clear-the-air meeting with the then enterprise minister Jonathan Bell.

But Mr Johnston, who is now the DUP's chief executive, has given the inquiry a completely contrasting account of the meeting.

BBC News NI

It is the scandal that sent Northern Ireland's devolved government up in flames and risked leaving taxpayers hundreds of millions of pounds out of pocket.

The RHI debacle has exposed serious flaws in the region's civil service and governance systems.

BBC News NI has followed every minute of the inquiry into the scandal since it started last autumn.

Read our review of some of the major revelations that have emerged so far.

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 developing political crisis surrounding the scheme.

The RHI Inquiry began in November 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 will look 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 2015
• the scheme's closure

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 it 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... and 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.

A chill wind whips across the Parliament Buildings car park up here on Stormont hill as the participants in the Renewable Heat Incentive Inquiry arrive for today's evidence session.

Image source, PA

After his inquiry debut yesterday, former Democratic Unionist Party (DUP) adviser Tim Cairns is back with more revelations about the inner workings of party and government.

The session kicks off shortly so stay with us for what should be an interesting day.