Two Stormont ministers were fighting like “alley cats” as public money caught up in Northern Ireland’s ill-fated green energy scheme disappeared, the chair of a public inquiry has said.

Sir Patrick Coghlin delivered a scathing assessment of the behaviour of the DUP and Sinn Fein as they struggled to agree a plan to limit the Renewable Heat Incentive’s (RHI) huge £490 million overspend.

Sir Patrick made the criticism as he heard evidence from former Sinn Fein finance minister Mairtin O Muilleoir.

Mr O Muilleoir and DUP economy minister Simon Hamilton were at loggerheads, with their civil servants failing to cooperate, in the heated final weeks before the collapse of powersharing in January 2017 amid the fallout from the RHI.

Mr O Muilleoir was required to rubber stamp proposals being developed by Mr Hamilton to reduce Stormont’s financial exposure to the scheme.

He told the inquiry he had asked his officials to “go to war” with counterparts from the Department of Economy to force them to come up with a workable solution.

He said relations with the DUP were at a “low ebb” at the time and every time party members engaged they “drew metaphorical daggers”.

The Sinn Fein MLA also branded former DUP first minister Arlene Foster a “disgrace” for unveiling her proposed solution in a newspaper article, presenting herself as a “saviour”.

Referring to the stand-off between Mr Hamilton and Mr O Muilleoir, Sir Patrick said they appeared more concerned with passing the blame than working together for the public good, with the ministers behaving like “alley cats”.

“What you would like to see here given the fact there is a clear threat to public funds and public money is a degree of positive cooperation, what you get is two alley cats fighting, walking around each other,” he said.

He said while the ministers were clashing “ordinary people in the street were losing money – disappearing every day”.

“If you are a man or woman on the street, it’s really disappointing not to see more co-operation,” he added.

“It’s looking for blame – who to blame, how to blame.”

Mr O Muilleoir defended his “robust” approach, emphasising how dire the political crisis was.

Mairtin O Muilleoir
Sinn Fein’s Mairtin O Muilleoir (Niall Carson/PA)

He said the peace process was “imploding”.

“This was the greatest political crisis of the last decade,” said the former minister.

He added: “At this time the DUP has become a byword for less than appropriate behaviour in relation to RHI.”

Mr O Muilleoir continued: “I apologise if you think we should have been more collegial at this point, but there is a crisis going on outside the hall, it involves the DUP, it involves the plummeting attitude of the public in the DUP and I can’t, even today, divorce my actions from my determination not to let the DUP say ‘well, it’s the Department of Finance’s fault as well’.

“So we pushed hard for a solution and I can only stand over that.”

Mr O Muilleoir also defended his party’s earlier efforts to delay the closure of the RHI.

He said he and colleagues were not aware of the scale of the financial mess caused by the RHI, or allegations of its misuse, when they demanded it was kept open for two more weeks in February 2016.

Mr O Muilleoir, who was not yet a minister at the time, had publicly called for the fortnight delay when the intention to close the RHI to new applicants was initially announced.

The scheme was ultimately left open for a further two weeks – a delay set to cost an estimated £90 million over the next 20 years.

Almost 300 new applicants signed up during that period.

Mr O Muilleoir said his party believed a sudden closure of the scheme would have been “unfair” on genuine business people.

He highlighted that the inflated tariff rates responsible for most of the scheme’s woes were no longer in operation when the closure debate unfolded.

The Assembly member said his party had “some knowledge” that the scheme was in “trouble” when the closure was originally floated, but was not aware of the extent of the problem.

“We were also aware that many people were saying that if you close this now you are going to do irreparable damage to our businesses,” he said.

He added: “It seemed to me to be unfair if genuine applicants had invested their money, if jobs were dependent on it, was there not another way, especially as we had been told the previous November the high tariffs had been removed.

“So we were trying to find a common ground.”

Earlier, Sir Patrick claimed Sinn Fein had “deliberately” breached a Stormont code on using special advisers.

He was referring to arrangements that led to key Sinn Fein adviser Aidan McAteer being paid with party funds, not public funds.

Mr McAteer was barred from holding an official special adviser role after 2013 legislation prevented convicted paramilitaries from filling the temporary civil service posts.

The party then decided to employ him as an adviser paid by the party coffers.

Sir Patrick said there was no question over Mr McAteer’s conduct as an adviser, but he said his role contravened a code which said that civil servants could not be directed by people paid by political parties.

Mr O Muilleoir defended the party’s decision, highlighting its opposition to the “discriminatory” 2013 law change.