Northern Ireland’s ex-first minister has denied responsibility for the province’s non-domestic Renewable Heat Incentive (RHI) even though she had departmental responsibility for the botched scheme.

Delivering her hotly awaited evidence on day 54 of the public inquiry into the scheme, Arlene Foster said she had “done nothing wrong” with respect to the scheme, which resulted in an estimated overspend of £700 million for the installation of renewable heat devices.

The scandal over the over-payments triggered the collapse of Northern Ireland’s power sharing administration in early 2017.

Foster expressed regret that Northern Ireland had not taken part in the UK-wide scheme rather than having its own bespoke scheme.

She also told the inquiry she had relied on officials to keep her up to speed on energy issues, which she admitted she found more “complex” and less interesting than other aspects of her portfolio at the Department for Enterprise, Trade and Investment (DETI).

In written evidence, submitted to the inquiry and published yesterday (12 April), Foster said she was “no longer” minister at Northern Ireland’s DETI by the time “problems or difficulties began to emerge” with the scheme.

While she acknowledged that communication took place about the RHI between DETI and the Department of Finance and Personnel (DFP) from May 2015, this was “not escalated to ministerial level.”

The Democratic Unionist Party leader said that when she was DETI minister there was “an underspend” in the non-domestic RHI scheme and uptake was slow. At the end of 2014, she said this underspend stood at approximately £15 million.

Foster claimed she became aware of the “true funding position” in late December 2016 or early January 2017 from HM Treasury by which time she was Northern Irish first minister.

She said she “suggested” to her successor at DETI that the scheme should be closed “as soon as reasonably practicable”.

But the first minister said she asked the DETI minister to delay the closure by “several weeks” following representations by a “number of public representatives that a little more time should be allowed before the scheme was closed.”

Foster acknowledged that “it is clear that there were a number of significant flaws with the scheme”.

The “crucial mistakes” included setting the tariff for small to medium biomass at a level higher than the cost of the fuel.

And she said that the inquiry is “best placed” to identify where responsibility lies for the flaws in the way the scheme was set up.

She also said in her written evidence that she felt no need to query the level of applications for the Northern Irish RHI scheme, which was 7 per cent of the total for the UK as a whole, two and a half times higher than would be expected on a per capita basis.

“There were no budgetary concerns flagged to me by officials about the NI applications being 7 per cent of the GB applications in the first year and I was not advised about the need to introduce budgetary controls.

“I understood that the scheme was being monitored by both Ofgem and the department and therefore if there had been any concerns, they would be brought to me.”

Foster will continue to give evidence today (13 April) at the inquiry which is taking place at Stormont House, the location of the Northern Ireland Assembly, which has been suspended since Sinn Fein’s withdrawal from the province’s administration.

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