The family of murdered Belfast solicitor Pat Finucane has lost a Supreme Court challenge over the decision not to hold a public inquiry into his killing, but won a declaration that an effective investigation into his death has not been carried out.

Mr Finucane was shot dead in front of his family in February 1989 by loyalists paramilitaries.

The 39-year-old was shot 14 times while eating Sunday lunch at home with his family.

His widow Geraldine claimed the British government unlawfully "reneged" on a promise to hold a public inquiry into the killing when former prime minister David Cameron instead ordered an independent review.

An investigation by former UN war crimes prosecutor Sir Desmond de Silva QC found "shocking" levels of state collusion involving the army, police and MI5, but ruled out an "overarching state conspiracy".

Today, just over 30 years on from her husband's murder, the Supreme Court in London ruled that Mrs Finucane had been given "an unequivocal undertaking to hold a public inquiry into Mr Finucane's death", but that the "change of heart on the part of the government" was made in good faith.

Giving the judgment of the court, Lord Kerr found that the decision not to hold a public inquiry into the murder was a matter for the government's "political judgement".

He also dismissed Mrs Finucane's contention that the decision was predetermined, stating: "There is simply no sustainable evidence that the process by which the decision was taken was a sham or that the outcome was predetermined."

But the court also ruled that the de Silva review was not compliant with Article 2 of the European Convention on Human Rights, which required the investigation to be provided with "the means where, if they can be, suspects are identified and, if possible, brought to account".

Lord Kerr declared that there has not been an effective investigation into Mr Finucane's murder, but added: "It does not follow that a public inquiry of the type which (Mrs Finucane) seeks must be ordered.

"It is for the state to decide... what form of investigation, if indeed any is now feasible, is required in order to meet that requirement."

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Speaking outside the court, Mrs Finucane said: "This is a historic moment. I stand before you today outside the United Kingdom Supreme Court with one simple message: we won."

She added: "The British government now knows that it cannot conceal the truth any longer. They have now been told this by the highest court in the land.

"It is time for the murder of Pat Finucane to be properly and publicly investigated in a public inquiry. Nothing less will suffice."

Her son John Finucane said the judgment was a "great result" for the family.

Speaking on RTÉ's Today with Sean O'Rourke, he said the court unanimously said that the British government had not met its obligations to provide an effective investigation and Downing Street must now be asked if it would do the right and honourable thing.

He said he expected that there would be engagement between his family and the government.

John Finucane said his family had become more used to setback than success and today's news had given them an enormous lift.

In a statement following the judgment, the Finucane family thanked the Supreme Court justices "for their careful and respectful consideration of the case" and welcomed the judgment that the De Silva review was not an effective investigation into the murder, and not compliant with Article 2 of the European Convention on Human Rights.

The statement added: "Two main factors led to the court's conclusion. First, all investigations to date have lacked the power to subpoena witnesses and, secondly, no one has been identified as being responsible for the collusion found by previous investigations and admitted by the government, i.e. conduct of state agents who facilitated and furthered the murder.

"The decision was unanimous. That is the end of the court process.

"The only lawful decision open to the government that can rectify this state of affairs is a decision to hold a public inquiry under the Inquiries Act that has the statutory power to subpoena witnesses and order the disclosure of all relevant documentation.

"We look forward to working in such an inquiry to assist in the search for the truth which is now thirty years overdue".

UK court ruling 'very significant' - Taoiseach

The Taoiseach has described today’s ruling as "very significant", and said that the Government's position remains that a public inquiry should be held.

Speaking in the Dáil, Leo Varadkar said that while the judgment found that the British government was acting within its power in deciding not to hold a public inquiry, it also found that the inquiries held to date were not adequate and not compliant with the European Convention on Human Rights.

"The government and I believe that finding is very significant," he said.

He was responding to Sinn Féin president Mary Lou McDonald, who said the British government had continually refused to honour its commitment to hold a public inquiry into Mr Finucane's murder.

"The position of the Irish Government is that the British government should now honour its commitment to carry out a public inquiry in accordance with the Inquiries Act, into the murder of Pat Finucane, the solicitor and human rights activist," Mr Varadkar said.

Ms McDonald said she "warmly welcomed" the Taoiseach's commitment to vigorously pursue the matter.

"I hope the British government on this occasion moves away from it's position of denial of the truth to the Finucane family," she said.

Also speaking in the Dáil, Tánaiste and Minister For Foreign Affairs Simon Coveney said the Government's position on the case has not changed.

"The Irish Government's position remains very consistent and very firm.

"There was an agreement here that there would be a full public inquiry established and that agreement has not been followed through on and we believe it should be. That position isn't going to change," he said.