Sinn Féin has again urged the British government to abide by court rulings ordering a public inquiry into the murder of GAA official Sean Brown in 1997.
A coroner, High Court judge and three judges in the Court of Appeal have all ruled that a public inquiry is the only lawful remedy.
The Irish Government has also backed calls by Mr Brown's family for a public inquiry.
But the British government last week lodged papers seeking the permission of the UK Supreme Court to appeal against an order mandating such an inquiry.
Am uncompleted inquest into his killing by loyalist paramilitaries heard that several British state agents were among 25 people linked by intelligence to the murder.
Speaking after meeting Northern Ireland Secretary of State Hilary Benn in Belfast this morning to discuss legacy issues, Sinn Féin's north Belfast MP John Finucane said the party had criticised the decision to appeal the ruling.
Asked if the Irish Government should make a public inquiry into the killing a "red line" issue in negotiations with the UK about how to deal with the legacy of Northern Ireland's Troubles, Mr Finucane said it was a legal issue, not a political one.
"It's not necessarily about what should be a political red line," he said.
He said: "It's what the courts have said, and the courts have made it very clear that the only vehicle that exists that can provide truth and justice and give Bridie and her family answers is a full public inquiry.
"That was made clear by the Coroner, it was made clear by a High Court judge, it was made clear by the Court of Appeal, and was endorsed also by our Chief Constable.
"So these are people independent of the Brown family who have all made that legal assessment, and I think that's the assessment that should be followed by the British government."
