The PSNI has failed in an appeal against an order to disclose police documents related to two murder attempts on a Catholic taxi driver.
The police admitted a claim of wrongdoing in public office in 2015 after being sued by John Flynn over two attempts on his life in the 1990s.
However, it appealed against an attempt to access police documents.
Judges dismissed the appeal and said it was hard to contemplate a more grave subject matter.
Mr Flynn has said the PSNI did not fully examine claims of security force collusion with loyalists.
A notorious UVF unit, based in Mount Vernon, north Belfast, is believed to be responsible for two attempts to murder Mr Flynn.
A gunman tried to ambush him as he picked up a taxi fare, and a bomb was placed under his car. It is alleged the attacker was a police informer.
'Long and tortuous history'
The PSNI argued that it had already admitted liability in the case and that producing the documents would be irrelevant, costly and divert resources from other cases.
However, judges at the appeal court said the full extent of police misconduct needed to be established before compensation for Mr Flynn can be decided.
The judges said discovery of documents in the case has a long and tortuous history, and that the PSNI should provide the papers as quickly as possible.
Mr Flynn's claim is linked to an investigation in 2007 by former police ombudsman, Nuala O'Loan.
That report found that members of the RUC Special Branch had allowed UVF informers to act with impunity, and that the Mount Vernon gang may have been involved in up to 15 murders.
Mr Flynn claimed Mrs O'Loan's successor, Al Hutchinson, did not adequately implement recommendations from the 2007 report to examine whether agents' handlers committed any crimes.