Three men acquitted of murdering a private investigator have won a claim against the Metropolitan Police for malicious prosecution.
Jonathan Rees, Glenn Vian and Garry Vian were charged following the 1987 killing of Daniel Morgan - but proceedings were aborted after a key piece of evidence was compromised.
The trio's attempt to sue the Met later proved unsuccessful.
However, the Court of Appeal has now overturned that decision.
Mr Morgan, originally from Llanfrechfa, near Cwmbran, was found outside the back of pub in Sydenham with an axe still embedded in his skull.
After the killing his family said the father-of-two was on the verge of exposing police corruption.
In 2008 Mr Morgan's business partner Mr Rees, the Vian brothers and a fourth man were charged with murder.
The Court of Appeal heard that a key "plank" of the prosecution case hinged on the evidence of a "known criminal" called Gary Eaton.
In the course of the process Mr Eaton, who also had a personality disorder, moved from being unwilling to name directly any of the participants in the murder to naming Mr Rees and the Vian brothers.
The four men spent two years on remand before the case against them was aborted and a formal not-guilty verdict was made by the judge.
In a written judgement, the Court of Appeal said the collapse of the case came after Met Det Ch Supt David Cook had had a "number of unauthorised" meetings with Mr Eaton.
Mr Rees and the Vian brothers sought damages from the Met - but their case was dismissed in the High Court in February 2017.
However on Thursday, judges said the three men should be entitled to compensation after being "maliciously" prosecuted.
Lady Justice King said: "To say that Det Ch Supt Cook, a prosecutor guilty of perverting the course of justice by creating false evidence against the appellants was, on account of his belief in their guilt, not acting maliciously, is rather like saying that Robin Hood was not guilty of theft.
"One understands the motivation in each case, but any seeming endorsement of such dishonest behaviour, particularly within the police force, leads... to a serious and unacceptable 'negation of the rule of law'."
Previously, Mr Morgan's family said it would be "a travesty of justice" if Det Ch Supt Cook was made a scapegoat "for the failures "of the Metropolitan Police's handling of Mr Morgan's murder.
The Metropolitan Police said it planned to launch a counter appeal with the Supreme Court.
Details of how much compensation the force will have to pay out has not been disclosed.