Arlene Foster’s former special adviser knew a “tsunami” of applications was about to swamp a botched green energy scheme, but could not recall passing the warning on, he told an inquiry.

DUP leader Mrs. Foster was finance minister at the time, in 2015, with control over the purse strings. Dr. Andrew Crawford was her main party helper.

The taxpayer bill for the RHI spiralled after a huge spike in applications in the weeks before cost controls were introduced later that year.

Dr. Crawford said: “I was telling them, there is a tsunami coming here, you need to move.”

Mrs. Foster, a Fermanagh and South Tyrone MLA, has said Dr. Crawford did not inform her of this.

A member of the public inquiry panel probing the matter, Dr. Keith MacLean, said: “It seems very strange that that would not be passed on.”

Dr. Crawford said: “I certainly didn’t keep it from her, but I can’t sit here today and say… I gave her the information.”

Evidence before the inquiry showed civil servants were aware the number of applications was increasing, and were moving to introduce cost controls.

RHI inquiry chairman Sir Patrick Coghlin told Dr. Crawford: “You had gone from Department of Enterprise, Trade and Investment (DETI) to Department of Finance and Personnel (DFP), you now knew that there is a tsunami of applications coming down the line, in a situation where DETI don’t have the approval from DFP to spend the money.”

Counsel to the inquiry Joseph Aiken asked what was wrong with Dr. Crawford putting his warning in an email to his minister.

Dr. Crawford responded: “I should have done it, looking at it now it seems something I should have done.”

Sir Patrick said the witness felt if Northern Ireland spent more than its fair share of the Treasury-funded scheme, he would have thought that would be to the country’s advantage.

Dr. Crawford said: “I was taking the view that there was a pot of money at a national level to support the RHI, Northern Ireland was going to go above its population share for that four per cent."

Reasons for the overspend could be the country’s more rural character, limited natural gas network and greater reliance on oil, the witness said.

He added: “A combination of all of those factors would have been a perfectly reasonable argument for us going above that four per cent figure.”

He spoke to an installer who told him of claims that empty sheds were being heated to maximise the subsidy paid, and passed those concerns on to the Enterprise Department.

Dr. Crawford resigned as special adviser following earlier RHI inquiry disclosures.

He said his brother James and two cousins who lived within 10 miles of him installed 11 wood fuel burners to heat chicken houses used to supply meat to producer Moy Park.

The witness denied any efforts to delay the imposition of cost controls on the massively over-spending scheme in 2015, as civil servants wanted to take action and he said the DUP wanted to unfairly “pin the blame” on him.

His evidence conflicts with that given by another former party special adviser to the public inquiry established to probe the matter.