Updated 6.04pm

NORTHERN IRELAND’S FIRST Minister Arlene Foster has strongly criticised the decision by Sinn Féin’s Martin McGuinness to resign as the North’s Deputy First Minister.

Foster, who is the leader of the DUP, said she was “disappointed” in McGuinness. “It is clear that Sinn Fein’s actions are not principled, they are political,” she said.

“Let me make it clear the DUP will always defend unionism and stand up for what is best for Northern Ireland and it appears from the Deputy First Minister’s resignation letter that is what annoys Sinn Fein the most,” she said.

In a letter sent to the speaker of the Stormont Assembly today, McGuinness said that he was resigning over the ongoing Renewable Heat Incentive (“cash for ash”) scandal, which has engulfed First Minister Arlene Foster.

On Saturday Sinn Féin leader Gerry Adams warned that an election would be called if Foster wouldn’t resign over the energy scandal. However, it is believed that the party’s Ard Comhairle last night and agreed a proposal that McGuinness would resign effective 5pm today.

The party says that it will not nominate a successor to McGuinness until after an election, which now seems imminent. Unless the party appoints a successor, the election will be triggered in seven days.

In the letter, McGuinness wrote:

“The DUP leader has a clear conflict of interest. She was the minister responsible for RHI scheme at its inception. No cost controls were put in place and warnings were ignored. This has led to an enormously damaging pressure on our public finances and a crisis of confidence in the political institutions.”

In a statement issued this afternoon he said:

Over the last ten years I have worked with DUP leaders and reached out to unionists on the basis of equality, respect and reconciliation. Over this period the actions of the British government and the DUP have undermined the institutions and eroded public confidence.

“Sinn Féin will not tolerate the arrogance of Arlene Foster and the DUP. Sinn Féin wants equality and respect for all. That is what this process must be about.

Today I tendered my resignation. Today is the right time to call a halt to the DUP’s arrogance.

“There will be no return to the status quo.”

'My health has absolutely nothing to do with this whatsoever', Martin McGuinness says as he announces resignation as Deputy First Minister. pic.twitter.com/mfOpqlKXp7 — RTÉ News (@rtenews) January 9, 2017 Source: RTÉ News /Twitter

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Dublin reaction

Reacting to the resignation of McGuinness, the Irish government has stressed what it says is the importance of protecting both the Good Friday Agreement and the Northern Ireland institutions.

Minister for Foreign Affairs Charlie Flanagan has said that he “regrets the circumstances” that have led to today’s resignation by McGuinness.

“The substance of the RHI controversy is very much a matter for the devolved executive and assembly. However, the government is very mindful of the need to protect the integrity of the principles and institutions of the Good Friday Agreement,” Flanagan said in a statement.

If, as appears likely, new elections to the assembly will now be required, it behoves all parties to act responsibly in word and deed, so that the political institutions of the agreement will not be damaged in the longer term.

Flanagan also said that today he has spoken to both McGuinness and Britain’s Secretary of State for Northern Ireland James Brokenshire.

Opposition parties

Echoing Sinn Féin’s blame of Foster for the current crisis SDLP Leader Colum Eastwood has also accused her of arrogance in how she has dealt with the questions arising from the ‘cash for ash’ scandal.

“The public understand that there is one reason for this potential election – Arlene Foster’s arrogance,” Eastwood said this evening.

The SDLP is ready to fight an election. Last May the Executive offered a Fresh start and have now failed – we will offer the public the chance of change.

Eastwood also said that the SDLP’s first priority following an electoral mandate would be a full inquiry into the Renewable Heat Incentive.

“Each and every day this scandal is costing taxpayers £85,000. If the executive is incapable of opening itself up to accountability, I would urge the electorate to enforce their accountability at the ballot box,” Eastwood said.

The Ulster Unionist Party (UUP) has criticised McGuinness’ decision to step aside, saying that having an election now would be “farcical”.

“This is not the way to resolve the RHI scandal. Sinn Féin should have stayed, to hold the First Minister to account, to force a public inquiry and to vote on the much-needed cost controls on the scheme,” according to UUP leader Mike Nesbitt.

Instead, they have prioritised self-interest, as always. This is Sinn Fein letting the DUP off the hook. The public mood clearly indicates they want the facts of the RHI debacle exposed. To move straight to an election without this taking place is farcical.

Cash for ash

In a BBC NI interview last month, DUP MLA Jonathan Bell claimed that he was met with a hostile reaction when he informed First Minister Arlene Foster that a government energy scheme was being abused.

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 Source: Gerry Adams /Twitter

The scheme’s overruns amount to the equivalent of half a billion euro. McGuinness and other Sinn Féin representatives repeatedly called on Foster to stand aside, but she refused to do so and survived a no-confidence motion.

The RHI scheme gave flat rate payment to use renewable energy, leading to people generating energy to earn money. It meant that businesses were paid more than they needed to be and there was perhaps a financial incentive to use extra fuel, hence the ‘cash for ash’ moniker.

- With reporting by Rónán Duffy