Senior police officers covered up illegal inducements given to a supergrass witness in a murder trial, allowing him to visit a brothel, take heroin and conduct a sexual relationship with a woman officer.
Despite evidence of a "prolonged, persistent and pervasive conspiracy to pervert the course of justice" three years ago, no prosecution or disciplinary action has been taken against any of the officers, a small number of whom are still serving with West Yorkshire Police.
The disclosures, which emerged yesterday in a Supreme Court judgment into the 1998 murder trial at which convicted criminal Karl Chapman was the star witness, reveal gifts, money and privileges given in exchange for his testimony against a former cell mate – none of which were revealed to the defence or the Crown Prosecution Service.
These included allowing Chapman, who was in jail awaiting sentence after admitting 267 counts of robbery, mainly against frail and elderly victims, to go to the pub and drink alcohol, smoke cannabis and socialise at police officers' houses.
He was allowed to enjoy unsupervised periods of freedom, given hundreds of pounds of spending money and offered a £10,000 reward for his cooperation. Describing a visit to a brothel, Chapman even apologised to the female officer with whom he was having an affair. "I was drunk and stoned on weed, they paraded a dozen beautiful women in front of me and said take your pick," he wrote.
A report by the Criminal Cases Review Commission, completed in December 2008, found that police also failed to investigate serious allegations of violence against Chapman, who had provided them with evidence against a former criminal associate.
These included the stabbing of a fellow prisoner, an alleged rape of a cellmate and an assault on the WPC.
The evidence emerged after a separate investigation into the conduct of West Yorkshire police during the prosecution by the neighbouring North Yorkshire force.
The Crown Prosecution Service said no action had been taken against any of the officers involved because there was "insufficient evidence for a prospect of conviction".
West Yorkshire Police yesterday referred the matter to the Independent Police Complaints Commission and said it would look again at events surrounding the original trial.
Paul Maxwell and his brother, Daniel Mansell, were found guilty in 1998 at Leeds Crown Court of murdering 85-year-old Joe Smales. The convictions were quashed by the Court of Appeal in 2009 on the grounds they been "procured by gross prosecutorial misconduct". The Supreme Court ruled that Maxwell should face retrial and last month he received a 17-year jail term after admitting the killing.