DUP MLA Jonathan Bell is set to sue First Minister Arlene Foster over comments she made about him when the pair appeared in an extraordinary TV show earlier this week.

An astonishing war of words erupted as they hit out at each other's handling of the 'cash for ash' scheme in separate interviews with the BBC's Stephen Nolan.

However, Thursday's clash has taken a new twist as Mr Bell was last night poised to launch legal proceedings against his party leader.

The former Enterprise Minister has instructed his solicitor Paul Tweed to sue Mrs Foster for defamation following comments she made during her BBC NI interview.

The First Minister made certain allegations about Mr Bell's behaviour during the course of the interview relating to his conduct generally and during a meeting with her concerning the botched energy scheme.

She alleged that the Jonathan Bell who appeared in the TV interview "is not a Jonathan Bell that would be familiar to many of his political colleagues, to many of his civil servants that he worked with in the department, or to many in the business community".

Mr Bell has robustly denied the First Minister's claims and has told friends that he is determined to pursue the matter in the courts.

When contacted by the Belfast Telegraph last night, Mr Tweed refused to comment.

The Strangford DUP MLA has given an entirely different account of the Stormont meeting in which he alleges there was a "hostile" atmosphere of "fear" and Mrs Foster was "highly agitated and angry" with him.

She has strongly denied his account.

In his explosive BBC interview, Mr Bell claimed that Mrs Foster had overruled him from immediately shutting down the catastrophic Renewable Heat Incentive (RHI) scheme, which will cost taxpayers an estimated £400m.

Mrs Foster has claimed that he is making the allegations to mask his own failings, and that he wanted to run the scheme for longer than she did.

Martin McGuinness yesterday called on her to "stand aside" as First Minister while the scandal was investigated.

The Deputy First Minister said he was concerned that "credibility of the political institutions is being undermined".

His intervention came after growing pressure from nationalist grass roots that Sinn Fein takes a tougher stand against the DUP on the issue.

Mr McGuinness told Mrs Foster that, in light of "allegations from a former DUP minister that there was corruption", it was in the public interest that she step down while an investigation was under way "at least until an initial assessment has been concluded into the veracity of all the allegations".

Mr McGuinness said that were he in the same situation, he would temporarily stand aside. The SDLP and the Ulster Unionists have already demanded that Mrs Foster step down.

In response to the Deputy First Minister's call, the DUP said that Mrs Foster "does not take her instructions from Sinn Fein, but from the electorate".

A party spokesman added: "The First Minister will not be stepping aside, but instead is focused on ensuring the full facts about this issue emerge and proposals are brought forward which can make a significant reduction in the future financial burden the Executive would face."

SDLP leader Colum Eastwood welcomed that Mr McGuinness had finally moved "to adopt the position of authority that Opposition parties have already taken". He added that "this is not a time for further equivocation".

Mrs Foster faces a Ministerial Exclusion Motion on Monday as the Assembly is recalled for a special sitting to discuss the growing political crisis. The SDLP secured the 30 signatures necessary to bring forward its motion to suspend the First Minister for six months to allow for an investigation.

The motion was supported by Ulster Unionist, Alliance, Green Party, People Before Profit and Traditional Unionist Voice Members.

Alliance leader Naomi Long said that a judge-led inquiry would be "the best way to uncover the truth on behalf of the public".

UUP leader Mike Nesbitt said that Mr Bell's "characterisation of Spads running the show" at Stormont was "consistent with my experience of how the DUP operates".

Belfast Telegraph