A SENIOR civil servant has admitted he cannot remember a scheme producing worse value for money than the renewable heat incentive (RHI).
It aimed to cut the cost of green energy to encourage people off fossil fuels but ended up landing ministers with an overspend of hundreds of millions of pounds.
Dr Andrew McCormick is permanent secretary at the Department of Economy.
He said: "It has given us more pause for thought than anything I can remember."
A lack of cost controls enabled businesses to claim huge sums of public money for running biomass boilers, with allegations of an "ash for cash" racket that saw some applicants claim vast sums for heating empty buildings.
The former Department of Enterprise, Trade and Investment (Deti, now the Department of Economy) designed the RHI.
Mr McCormick said ever since he was a junior civil servant in the department of finance in the 1980s he had been taught to ask why repeatedly and that had not happened in this case.
"I cannot recall anything that was on the scale in relation to both opportunity costs to public services and... poor value for money," he said.
Millions will have to be set aside annually to cover the cost of the 20-year scheme.
Mr McCormick reassured Public Accounts Committee (PAC) members at Stormont that lots of mechanisms in the government did work following decades of learning.
Committee member Daniel McCrossan said: "This is an unprecedented scandal beyond belief.
"It has damaged the credibility of this institution."
Overall, more than £1 billion of public money will be paid to Northern Ireland-based businesses by 2036 after they installed new appliances under the RHI scheme, which is now closed.
The RHI encouraged the installation of costly eco-friendly heating systems by paying a tariff per kilowatt of heat burned over a 20-year period.
Thousands signed up to the scheme, which started in 2012 and was extended to domestic customers in 2014.
According to whistleblower claims, a farmer is allegedly in line to receive £1 million over the next 20 years for heating an empty shed while large factories in Northern Ireland are also allegedly on course to pocket £1.5m over two decades for running incentivised biomass boilers all year round in premises that previously were not heated.