Stormont was thrust back into potential crisis on Monday after deputy first minister Martin McGuinness said Sinn Féin will now oppose the passage of the welfare bill in the Northern Assembly.

Crisis was averted at Christmas when Sinn Féin said it would remove its hitherto staunch opposition to British government welfare reform which thus facilitated the striking of the Stormont House Agreement.

Sinn Féin said it did its U-turn on welfare reform based on commitments that the affects of welfare cuts would be cushioned for the most vulnerable.

However Mr McGuinness accused the DUP of “acting in bad faith” on welfare protections and said that Sinn Féin will oppose the bill in the Assembly later today.

In an early response, DUP MP Jeffrey Donaldson in turn said Sinn Féin would itself be reneging on a deal if it now voted against the welfare bill. “The stakes couldn’t be higher,” he said.

Mr McGuinness said Sinn Féin had honoured its commitments and had worked constructively to put in place the welfare protections agreed last December.

“This package protects children with disabilities, adults with severe disabilities, the long-term sick and children in large families. We have been clear that the enactment of these protections is a red line issue for Sinn Féin,” he said.

“However, the DUP have acted in bad faith and are now reneging on their commitments to protect the most vulnerable. It is their intention to provide only partial protection to current recipients of benefit and no protection whatsoever for future claimants,” he said.

Most vulnerable

He said Sinn Féin would not be part of any agenda that punished the most vulnerable. “The DUP have attempted to effect Tory welfare cuts by subterfuge but at the heart of this crisis is the ideologically driven attack on the welfare state by the Tory-led government in London,” he said.

“If the DUP want to strip benefits from children with disabilities, from adults with severe disabilities, the long-term sick; or push children further into poverty, then they need to explain and justify that. Sinn Féin certainly will not accept that approach,” he said.

Mr McGuinness said until the DUP social development minister Mervyn Storey gave “effect to the intent of the Stormont House Agreement by providing full protection for current and future claimants; Sinn Féin will not be in a position to support the Welfare Bill going through the Assembly”.

Mr McGuinness has 29 Assembly members. It needs support from one other Assembly member to pursue a petition of concern which would be an effective veto on the welfare bill.

After delivering his press conference the DUP MP, Mr Donaldson told BBC Radio Ulster that if the welfare bill was rejected then the consequences would be “massive” and politics in Northern Ireland would be in “very, very troubled waters”.

First minister Peter Robinson stated previously that if there was not a deal on welfare reform then the Northern Executive and Assembly could hardly survive.

Failing to pass the welfare reform bill could lead to the British government re-imposing multi-million pound penalties, the loss of planned powers for the executive to set its own corporation tax rate and the possible collapse of Stormont.