Failures by the police and prosecutors to disclose evidence that could undermine a case or help a defendant risk jeopardising the chance of a fair trial, according to inspectors.
A review by HM Inspectorate of Constabulary (HMIC) and HM Crown Prosecution Service Inspectorate (HMCPSI) found examples of poor practice by both police officers and prosecutors in crown court cases.
HMCPSI chief inspector Kevin McGinty said the findings would "surprise no-one" working in the system and said there needed to be a "cultural change" in both services.
Inspectors examined 146 crown court case files, including 56 that the CPS identified as failing as a result of disclosure issues.
They found it was "rare" for police officers to tell prosecutors about evidence that could undermine their case or assist the accused’s – known in legal terms as unused material – and their recording of sensitive and non-sensitive evidence was "routinely poor".
Prosecutors in turn were "failing" to challenge the poor recording of material and carry out their duty to consider what to hand over to the defence throughout a case, leading to delays and even to trials collapsing.
The report said: "The failure to grip disclosure issues early often leads to chaotic scenes later outside the courtroom, where last minute and often unauthorised disclosure between counsel, unnecessary adjournments and – ultimately – discontinued cases, are common occurrences.
"This is likely to reflect badly on the criminal justice system in the eyes of victims and witnesses."
Inspectors found that in 81 (55.5%) of the cases they reviewed there were obvious disclosure issues before a defendant was charged, with prosecutors dealing with them fully in only one in four cases and in 38.3% of cases they were not dealt with at all.
The report gave an example of a man accused of robbery who protested he was in fact the victim of a violent drug dealer.
Neither the police nor the CPS investigated the defendant’s claim before he was charged and held in custody for six months and it was not until just before the trial that a review discovered police intelligence that corroborated his claim, leading to the case being dismissed.
The inspectors also said the audit trail for recording disclosure decisions "falls far below any acceptable standard of performance".
They made nine recommendations, including that the police and CPS put plans in place to identify issues before charges are brought and issue new guidance on training for officers.
The report’s authors concluded: "Until the police and CPS take their responsibilities in dealing with disclosure in volume cases more seriously, no improvement will result and the likelihood of a fair trial can be jeopardised."
Mr McGinty said. "A failure to deal effectively with disclosure has a corrosive effect on the criminal justice system. It undermines the principles of a fair trial which is the foundation of our system. It adds delay, cost and increases the stress faced by witnesses, victims and defendants.
"The findings of this inspection will surprise no-one who works within the criminal justice system as there appears to be a culture of defeated acceptance that issues of disclosure will often only be dealt with at the last moment, if at all. If the police and CPS are ever going to comply fully with what the law requires of them by way of disclosure, then there needs to be a determined cultural change.
"This is too important to be allowed to continue to fail."
Gregor McGill, director of legal services at the CPS, said: "The CPS understands the importance of complying with its statutory obligations relating to the disclosure of unused material and is committed to doing so.
"We will urgently work with our partners in policing, and other agencies, to address the findings in this report.
"We are already working with the police to improve our performance. For example, we are bolstering the role of our disclosure leads across England and Wales who ensure compliance with the mandatory disclosure regime and now insist on mandatory training for all our prosecutors.
"We know there is more to be done and will be taking a range of steps, which we will outline in a joint CPS and police action plan later this year."