Arlene Foster will give evidence on Tuesday to a public inquiry into Northern Ireland’s botched green energy scheme.
Questions over the Democratic Unionists’ handling of the overspending Renewable Heat Incentive (RHI) led to the collapse of political powersharing at Stormont early last year.
The DUP’s former coalition partners Sinn Fein have refused to retake their seats around the ministerial table and endless rounds of negotiations have not persuaded them.
Mrs Foster was enterprise minister when the flawed RHI scheme was being designed.
Controls to limit the scheme’s costs were not introduced and overly generous subsidies saw the taxpayer bill spike dramatically.
Mrs Foster has contested claims by a successor minister, former party colleague Jonathan Bell, that she asked him to keep the scheme open.
After Mr Bell’s allegations were made public Mrs Foster was asked by Sinn Fein to step aside from her role as Stormont’s first minister.
When she refused the late Sinn Fein deputy first minister Martin McGuinness resigned and triggered the collapse of the devolved institutions.
Mrs Foster has denied claims there was a party narrative from the DUP to discredit Mr Bell over the RHI scheme.