Legal action launched by the Irish Government against the UK’s controversial Legacy Act will complement challenges from Troubles’ victims in Northern Ireland, Sinn Fein leader Mary Lou McDonald has said.

Mrs McDonald said the legislation, designed to deal with the legacy of the Troubles in Northern Ireland, was a “flagrant breach of international human rights law”.

However, Ulster Unionist leader Doug Beattie said the Irish Government had done nothing itself to address the legacy of the Troubles.

Ireland’s deputy premier Micheal Martin said on Wednesday that his Government would initiate an interstate case against the UK on the grounds that the provisions of the Northern Ireland Troubles (Legacy and Reconciliation) Act 2023 are incompatible with the UK’s obligations under the European Convention on Human Rights.

Aspects of the laws, which received royal assent in September, include a limited form of immunity from prosecution for Troubles-related offences for those who co-operate with the new Independent Commission for Reconciliation and Information Recovery (ICRIR).

The Sinn Fein leader said: “Victims and families have been stating from the outset that this cruel and shameful Act is a flagrant breach of international human rights law.

“The British Tory Government rushed through this legislation despite the clear opposition and concerns raised by victims and families, all political parties, the Irish Government, the US, UN, the Council of Europe and human rights experts.

“It is a blatant attempt to shut the door on families’ efforts to achieve truth and justice through the courts and to give an amnesty to British state forces involved in the murder of, and serious human rights violations against, Irish citizens.

“Heartbroken families have been fighting for years, determined to get truth and justice for their loved ones. They should not have been forced to take individual legal actions against this Act, and this action by the Government will now complement these challenges.

“We will stand with those families as they challenge this cruel and cynical law, and as they continue to campaign with dignity and determination for truth and justice.”

SDLP leader Colum Eastwood said the Irish Government move was “utterly necessary”.

He said “no political party or institution on this island supports” the Act, describing it as “the most extreme legislation that shuts down access to justice for victims and survivors”.

“The British Government has clearly undermined the international treaty entered into as part of the Stormont House Agreement, they have fought political leaders from every party in the North and they have set themselves against the needs of victims and survivors,” he said.

“The inter-state case being taken by the Irish Government is both welcome and utterly necessary.

“If the British Government will not respect the treaties it enters into, respect international law or respect the basic tenets of justice then it must be challenged robustly.”

Mr Beattie said the move by the Irish Government was not surprising.

He said: “With an election year on the horizon they will have taken that opposition attack line off the table.

“This might sound cynical, but the reality is the Irish Government have done nothing to address the legacy of our past, they have refused to open parallel mechanisms or deal with the very real fact that Ireland was not an innocent bystander in the Troubles.”

He added: “Any interstate case will go through the courts and there will be an outcome at the end.

“But if both the United Kingdom Government and the Irish Government are not willing to fix the wrongs of the past then it will be the victims who suffer once again.”