Northern Ireland's deputy first minister Martin McGuinness has resigned.
McGuinness has helped to lead the assembly in Belfast since 2007, but is stepping down over first minister Arlene Foster's handling of a growing scandal involving incentives provided to businesses to use renewable heat systems, such as biomass boilers, on their premises.
In his resignation letter, McGuinness said: "The first minister has refused to stand aside, without prejudice pending a preliminary report from an investigation. That position is not credible or tenable."
McGuinness is calling for a fresh election "to allow the people to make their own judgement on these issue democratically".
Assembly rules mean that if Sinn Fein refuse to nominate a replacement for McGuinness, the Northern Irish secretary must call an election.
Ten years of valient service in Office Of First&DeputyFirst Minister Martin McGuinness signs resignation letter. GRMA chara 4 all Ur work. pic.twitter.com/1i4ezDTF5h— Gerry Adams (@GerryAdamsSF) January 9, 2017
The Renewable Heat Incentive scheme was launched by the Northern Irish assembly in 2012, with a target of 10 per cent of heat generation to come from renewable sources.
It was launched by the department for enterprise, trade and investment, at that point run by Foster as a government minister.
However, after officials announced plans to cut the subsidy - which was often more than the amount being paid for fuel - applications dramatically increased, and a subsequent inquiry into the spike led Northern Ireland's auditor general to warn that there had been no upper limits to the amount of subsidy that the Assembly would provide. It is believed the scheme could ultimately cost Northern Irish taxpayers up to £490m.
While applications to the scheme have been closed, it continues to pay out to almost 2,000 successful claimants, and up until today Sinn Fein had been pushing for an in-depth investigation of the failures in the creation of the programme.
The DUP said it would submit to an inquiry but Foster would not step down.