The Government last night appealed for calm in Stormont in the wake of Mr McGuinness’ resignation.
Foreign Affairs Minister Charlie Flanagan said he “regretted” the circumstances which have led to Mr McGuinness’ decision.
“The Government is very mindful of the need to protect the integrity of the principles and institutions of the Good Friday Agreement.
“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.”
Mr Flanagan spoke to Mr McGuinness and also to the British Secretary of State to Northern Ireland James Brokenshire.
“As a co-guarantor of the Good Friday Agreement, the Irish Government will continue to work with the British government and the political parties to advance political stability, reconciliation and economic prosperity in Northern Ireland,” Mr Flanagan added.
Fianna Fáil leader Micheál Martin said it is with a sense of dismay that he has watched the so-called ‘cash for ash’ scandal unfold.
“It was my hope that an agreement could be reached to facilitate a robust inquiry into this scandal.
“However, the decision of Mr McGuinness to resign his position and Sinn Féin’s demand for new elections means that will now happen. Instead, the stage is now being set for a bitter election campaign that will not address any of the issues that led us to this point, and the future of the institutions is thrown into serious doubt.”
Mr Martin said Sinn Féin’s decision would appear to do very little to address any of the underlying problems, and does nothing to deal with the challenge of limiting taxpayer exposure.
SDLP leader Colum Eastwood said the public understand that there is one reason for this potential election — Arlene Foster’s arrogance.
“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.”
“The public also knows that those behind ‘cash for ash’ scandal can now enjoy a two month break from any effective public inquiry or police investigation.
“The Sinn Féin statement references the attacks by the DUP on Irish identity and culture, and on the equality agenda. All of those statements and sentiments are true and I agree with them all.
“The DUP have governed disgracefully and it has extended well beyond the leadership of Arlene Foster.”
Ulster Unionist Party leader Mike Nesbitt said Mr McGuinness’ resignation was not the way to resolve the 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.
“Instead, they have prioritised self-interest, as always. This is Sinn Féin 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. They had a choice between the integrity of the institutions and electoral advantage and they appear to have chosen the latter. This is simply further proof of the DUP and Sinn Féin’s inability to govern. This scandal prone executive has had 10 years to get it right, that’s longer than most get in a mature democracy. They promised a fresh start, but delivered a fresh crisis of momentous scale.”
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
What happens now?
The first and deputy first minister have ceased to hold office but may still exercise their functions for a week.
If Sinn Féin fail to nominate a replacement for Martin McGuinness within seven days, elections will be called by Northern Ireland secretary James Brokenshire.
Some sort of talks process is likely after he said the parties should work together to find a way forward.
Why did McGuinness resign from his post?
He had warned of “grave consequences” if Arlene Foster did not temporarily step aside to allow a fully independent inquiry into the Renewable Heat Incentive scheme.
The government-subsidy scheme was set up in 2012 by the then economy minister to encourage businesses to switch from burning fossil fuels to greener sources like wood pellets.
Why did it run into trouble?
It was supposed to pay a proportion of fuel costs, but tariffs were set too high, meaning for every £1 participants spent on fuel, they received £1.60 in subsidy payments.
Claims of widespread abuse include a farmer allegedly set to pocket around £1m in the next 20 years for heating an empty shed.
Cost controls were incorporated into a similar scheme in Great Britain, but were absent in the North.
The total cost is projected to be more than £1bn over the next 20 years.
While the Treasury will pick up the bill for most of it, an expected overspend of around £490m will not be covered and will come out of the North’s block grant .
What happened when cost controls were announced?
A move to introduce a tiered payment scheme in 2015 was met by a flurry of applicants trying to get on to the old system before the date set for the changes.
Almost 1,000 applied in three months — around the same number from over the previous three years.
Opposition politicians have demanded answers around the spike.
When the cost controls were introduced, the scheme limped on for a further three months but, after the Treasury made clear it would not pick up the overspend bill, it closed for good in February.
What was Foster’s role?
As economy minister, she was in charge of the department that developed the RHI from 2012 to 2015.
Much of the scrutiny has focused on how she responded to concerns raised by a whistleblower during that time.
There was a flurry of claims about whether the individual raised concerns directly to Foster, or if she only outlined them after the DUP stalwart passed her on to meet officials.
The DUP published an email sent from the whistleblower to Foster that made no mention of her RHI concerns.
However, another email has since emerged, sent directly to Foster in 2013, that raised specific concerns about the scheme.
Why has Foster’s successor in the department been making headlines?
After she left the economy portfolio, DUP MLA Jonathan Bell took on oversight of the scheme and ultimately closed it.
He levelled a series of allegations against Foster and party advisers in an explosive TV interview.
He claimed he tried to pull the shutters down sooner but was dissuaded by Foster and other DUP advisers.
Foster disputed his account and said she acted to close it sooner.
She has accused her opponents of misogyny and said the party was working on steps to recoup the money.