First Minister, Arlene Foster

The email raises serious questions about the accuracy of information being put forward by the DUP about a scandal which civil servants say will cost taxpayers about Â£400 million.

Last week the DUP released the first email which the 'whistle-blower' sent to Mrs Foster's department in 2013. The email was essentially a business proposal and clearly did not contain allegations about the RHI scheme. The party demanded that "scurrilous" claims about what Mrs Foster knew were retracted.

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DUP deputy leader Nigel Dodds said five days ago: "In fact the 2013 email from the lady in question raised no concerns about RHI.

"It simply asked for a meeting on energy efficiency matters. A meeting with officials was facilitated and it was in these subsequent discussions that issues about RHI were conveyed. Mrs Foster did not attend these meetings or hear of the concerns. The initial email was the only contact with the Minister."

Mrs Foster personally set out the same position during her interview last Thursday with Stephen Nolan.

She said: "When I returned, we have finally found the letter that the lady sent to me and indeed it wasn't a whistle-blowing letter.

"The whistle-blowing was raised in later correspondence and in later meetings with the various officials that she met."

Mr Nolan asked: "So, you did receive allegations or not?"

Mrs Foster replied: "No, I didn't receive allegations; all I received..."

Mr Nolan said: "You said you told Spotlight..."

The First Minister responded: "I said I passed on the concerns the lady had raised with me."

Mr Nolan interjected: "No you did not. No you did not. Detail, First Minister. You said 'a whistle-blower made allegations to me' - your words."

Mrs Foster said: "Yes, because that's what was said to me by Spotlight. It now turns out that the lady only made those whistle-blowing concerns to the officials later on."

But this morning BBC Radio Ulster's Nolan Show revealed the contents of the whistle-blower's emails.

The email explicitly warned Mrs Foster about the disastrous problem at the heart of the scheme.

She said: "It pays them to use as much as they can. In fact, the incentive to use more is leading to misuse in some cases".

Ulster Unionist leader Mike Nesbitt described the emergency for the email as "the real final smoking gun, the nail in the coffin" for Mrs Foster.

The DUP told the programme that Mrs Foster could not find the email in her personal account because her records do not go back that far.

A DUP spokesman said: “As has been apparent over recent days there is clearly some confusion over the precise details in relation to the emails.

"The First Minister has no formal record of any emails from this period as her records do not go back this far.

"The First Minister initially indicated to Spotlight that she had passed on an email in relation to RHI to her departmental officials.

"Subsequently the First Minister was shown the email of 26 August 2013 from the person in question which was published last week. That email had been passed to officials, and the Minister had then replied to the person in question on 5 September 2013 offering a meeting with officials.

"Before the email of the 26th August was published the person who had sent the email was contacted by an official in the Department of the Economy who confirmed that the 26th August email had been the only direct contact with Arlene Foster, and the official’s understanding was that she was content to release that email subject to redactions.

"We apologise if there was any misunderstanding, as we certainly would not have released the email had we thought that would be against her wishes.

"However, we understand that another email has come to light dated September 30 which makes a reference to concerns about the RHI.

"The First Minister’s office has no record of this email, but equally no reason to believe that it was not sent or received.

"In any event the person in question contacted officials two days later on 5 September 2013 (in immediate response to the letter from the Minister) in order to set up a meeting at which her plans and concerns were discussed.