Police files must be disclosed in a major legal action over alleged collusion with a loyalist paramilitary agent suspected of up to 15 murders, the Court of Appeal has ruled.
Senior judges also cleared the way for a substantial pay-out to a north Belfast man who sued after surviving two UVF attempts on his life.
Confirming the level of damages achievable by John Flynn will not be bound by English cases, Mrs Justice Keegan said: "We find it hard to contemplate a more grave subject matter."
Mr Flynn's lawyers described the verdict as a huge development in legacy litigation.
The 57-year-old issued proceedings against the PSNI over murder bids allegedly carried out by an agent who operated in the city's Mount Vernon area.
In 1992 a gunman tried to shoot him after he was lured to Whiteabbey Hospital on the outskirts of the city.
Five years later a second attempt was made to kill him in a failed car bomb attack.
Mr Flynn brought a lawsuit against the Chief Constable for alleged negligence and misfeasance in public office.
In 2014, the PSNI admitted his misfeasance claim and accepted he should be paid damages.
But the force emphatically denies negligence or having ever employed the covert human intelligence source - identified only in the case as 'Informant 1'.
The agent is suspected of involvement in 10 to 15 murders, punishment shootings, serious beatings, conspiracy to murder, robbery, hijackings and drug dealing.
Mr Flynn's action was triggered by the findings of Police Ombudsman Nuala O'Loan that some Special Branch officers colluded with loyalist killers.
Her Operation Ballast report, issued back in 2007, centred on the activities of a UVF gang allegedly led by Mount Vernon man Mark Haddock.
As part of the lawsuit Mr Flynn's lawyers are continuing to seek access to PSNI documents.
They argued the police admission of partial liability was a tactical move to avoid handing over all files on the informant and cover over the full extent of alleged collusion.
An affidavit filed by Mr Flynn claimed police either failed to arrest the agent for the murders and other crimes or else conducted "sham" interviews, despite knowing he was a leading UVF figure.
Misleading records were deliberately compiled, while other documents and forensic exhibits were either destroyed or lost, he alleged.
Mr Flynn also claimed: "I believe that the police knew I was at risk from Informant 1 and were quite content to let me be murdered by him and his associates."
Last year a High Court judge ordered the handover of 13 categories of police documents.
Counsel for the Chief Constable appealed his decision, insisted it was an unnecessary step when Mr Flynn has effectively won the case.
The material being sought covers a period of more than a decade.
Appeal judges were told it would take years to identify all the files and comply with the level of discovery being sought.
A Public Interest Immunity (PII) process alone would cost in excess of £300,000, according to a Superintendent asked to assess the scale.
Around 1,500 documents were said to relate to Informant 1.
But dismissing the appeal, Mrs Justice Keegan, sitting with Lord Justice Gillen, stressed the significant context of the action.
"This case relates to alleged activities of informers acting within the structure of the State which resulted in significant harm to persons such as the plaintiff," she said.
Discovery of the documents was also held to be necessary for any assessment of damages.
The judge pointed out that work would already have been undertaken for the Ballast report, and described it as "astonishing" that the PSNI has not contacted the Police Ombudsman's Office to obtain information previously provided to it.
She added: "We do not see that the English cases referred to us regarding exemplary damages form a bind code in terms of the level of achievable damages.
"We consider that there is a valid argument that the subject matter of these proceedings extends beyond those bounds."
Outside court Mr Flynn's solicitor claimed the ruling was a resounding message that there will be no cap on the level of compensation for collusion cases.
Claire McKeegan of KRW Law said: "This judgment is hugely significant not only to the matter at hand but to all legacy litigation where the state representatives have cited resources as justification for non-compliance with the rules and have made nominal offers of compensation to victims.
"The Court of Appeal have today set a marker that this position will not be accepted."