The family of murdered GAA club chairman Sean Brown has criticised Northern Secretary Hilary Benn for appealing a court order requiring the establishment of a public inquiry into his death.
The appeal was lodged on New Year's Eve with the Brown family describing the move as "shameful" and that it was denying justice to his 87-year-old widow Bridie.
In mid December, Northern Ireland's High Court ruled that there was no viable alternative to the establishment of a public inquiry.
The judge ruled that the UK government was under a "clear and unambiguous obligation" to establish a statutory probe into the killing which involved loyalists working as state agents.
The family said it would continue to pursue justice and the decision to appeal the judgment posed serious questions about the information held by the UK authorities on the murder.
In a statement, they said: "Why does the Ministry of Defence and the security service in London hold documentation about the murder of a totally innocent family man who was simply locking the gates of his beloved GAA club in Co Derry.
"What was the relationship between these bodies and the LVF leadership?
"What was known in advance of the murder?"
Mr Brown was abducted and murdered by the Loyalist Volunteer Force as he locked the gates of Bellaghy Wolf Tones GAA club in south Derry in May 1997.
The 61-year-old father-of-six was driven to a country lane near Randalstown and shot six times.
No one has ever been convicted of his murder.
Last year, during a now discontinued inquest, it emerged that state agents were among more than 25 people linked by intelligence to the killing.
The coroner was forced to halt proceedings due to the volume of confidential material excluded or withheld on national security grounds.
The coroner wrote to the then-Conservative government urging the establishment of a public inquiry.
Last September, Mr Benn confirmed those calls had been rejected and he urged the Brown family to engage with the Independent Commission for Reconciliation and Information Recovery - a new body set up under the controversial Northern Ireland Legacy Act.
Although the Labour government has promised to repeal the act, it intends to retain the commission.
'Real blockage is in London' - Brown family
The Brown family said that with the courts recommending a public inquiry and the PSNI indicating that it would not oppose such a move, it appeared that the "real blockage is in London".
They said they could not understand why the security services and UK Ministry of Defence were being consulted on the appropriateness of a public inquiry.
They said: "This raises profound and deeply concerning questions about collusion and the role of state agencies in this case.
"As a family we want to put the Secretary of State on notice that we will not give up our struggle to get to the truth.
"We had hoped that he would take a different path to previous Tory ministers. Sadly this would appear not to be the case."
A Northern Ireland Office spokesperson said: "We have enormous sympathy for Mrs Brown and her family who have suffered so much since Sean Brown's murder.
"The recent judgment by the High Court however raises a number of important issues, including matters of constitutional significance that go beyond this individual case.
"The government has therefore lodged a notice of appeal to the Court of Appeal and we are seeking expedition.
"We are also seeking expedition of the application for permission to appeal to the Supreme Court in the prior case of Dillon & Others, which touches on related matters, so that all these issues can be considered as soon as possible.
"This appeal will not delay the government's determination to repeal and replace the Legacy Act, and to reform ICRIR to strengthen its capacity to find answers for victims and families."
