In February, the High Court in Belfast ruled elements of the legislation, which were passed into law last September, were in breach of European human rights laws.

The Northern Ireland Troubles (Legacy and Reconciliation) Act offers conditional immunity from prosecution for Troubles-era offences.

However, it's strongly opposed by all parties in Northern Ireland, victims' groups, and the Irish government - which has taken an inter-state case against the UK to the European Court of Human Rights.

From 1 May, all civil cases and inquests that were not at their findings stage were halted.

Responsibility for investigating all legacy cases has since been transferred to a new truth recovery body, the Independent Commission for Reconciliation and Information Recovery (ICRIR).

Opening the challenge to the February ruling at the Belfast Court of Appeal, barrister for the government Tony McGleenan KC summarised a number of previous unsuccessful attempts to deal with the legacy of the Troubles since the Good Friday Agreement was signed in 1998.

Labour Party leader Sir Keir Starmer has promised to repeal the legislation if his party forms the next government.

Speaking outside court, Martina Dillon, whose husband Seamus was murdered by loyalist terrorists in 1997, said she "had no choice" but to trust in Sir Keir's promise that Labour would repeal and replace the Legacy Act.

"I have to trust them", she told Sky News. "What else can I do? They [Labour] have said they would give us back our inquests, and we'll continue to fight on."

Grainne Teggart, of Amnesty International, urged the next government to ensure "rights and the rule of law will be respected, protected and upheld".

"We urge the next government to listen to the calls from victims, to do the right thing and overturn this law as a priority," she said.

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The High Court judge, Mr Justice Colton, said in February he was satisfied the provisions of the act that offer immunity from Troubles-era prosecutions breached Articles 2 and 3 of the European Convention on Human Rights.

However, he also ruled that the new Independent Commission for Reconciliation and Information Recovery (ICRIR) set up by the act was capable of making effective investigations and was not in breach of human rights law.

That ruling is itself being appealed by a number of victims' relatives today.

It's likely the outcome of the proceedings at the Court of Appeal will be challenged in a higher court.