Green Party leader Steven Agnew raised realy concerns about the RHI rules. Picture: Brian Little/Presseye

The question was asked in the Assembly by Green MLA Steven Agnew in July 2013 – just months into the RHI scheme.

In the Assembly on Monday, Mrs Foster said that “no one in government or in the Assembly in their work in creating and passing the legislation picked up on that crucial failing [that running boilers was profitable]. Contrary to some accounts, in the early years of the scheme, that was not widely picked up by the industry either.”

DUP colleauge Simon Hamilton also told MLAs: “I am happy to say that no one – not politicians, civil servants or external consultants – spotted the flaws.”

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However, Green MLA Steven Agnew did seem to grasp that there was a flaw in the scheme which was detracting from what should have been its environmental benefits.

In a written Assembly question to Mrs Foster in September 2013, he asked “for her assessment of whether subsidies for biomass disincentivises energy efficiency; and if so, what measures can be taken to combat this”.

Mrs Foster replied that her department was “very keen to promote energy efficiency alongside incentives for renewable heat technologies”.

Speaking of the domestic RHI scheme, she said that “DETI has included energy efficiency assumptions that will ensure that the tariffs are most appropriate and most beneficial for those that have already carried out energy efficiency improvements in their homes”.

And in relation to the non-domestic scheme – where the grossest abuses have taken place – she set out an assumption which it is now clear was incorrect. Mrs Foster said that “within the existing RHI for commercial premises it is assumed that the installation of a biomass boiler, or another renewable technology, would be the final action taken by a business seeking to become ‘low-carbon’, with the costs involved in installing renewable heating much greater than those involved with simple energy efficiency measures”.

Speaking yesterday, Mr Agnew said: “As far back at September 2013 I raised the issue of perverse incentives of the RHI scheme with Arlene Foster. This was dismissed out of hand by the now first minister. In fact, it was suggested that this scheme would encourage people to use less biofuel and improve their energy efficiency.