Evidence is being hidden and deliberately withheld in a "very worrying" failure of disclosure by police and prosecutors, a Freedom of Information request has revealed.
The Centre for Criminal Appeals (CCA) has obtained documents which reveal a significant and "perennial" problem with the repeated view that defence teams are not entitled to see all the evidence.
Several cases have recently been abandoned due to late disclosure of evidence.
The charity collected focus group notes from police, prosecutors and the judiciary, and survey responses from prosecutors.
They revealed concerns over "fragmented and inconsistent" disclosure training for police, and a "huge communication gap" between the police, prosecutors and the judiciary, with one judge calling the system "broken."
A response from a judge read: "The theme of withholding information is very worrying.
"There seems to be an idea that the defence is not entitled to see things but where the defence press matters, this yields results."
An extract from a CPS survey on disclosure said: "In even quite serious cases, officers have admitted to deliberately withholding sensitive material from us and they frequently approach us only a week before trial.
"Officers are reluctant to investigate a defence or take statements that might assist the defence or undermine our case."
The notes showed repeated references to the MG6D, which is a list of sensitive, unused material, being a place to store information that they did not want the defence to see.
At least one police force appears to have trained their officers to hide items on the MG6D.
The charity is calling for an independent disclosure agency to be established, which they hope would prevent wrongful convictions.
National Police Chiefs’ Council Lead for Criminal Justice, Chief Constable Nick Ephgrave said: "National training and guidance on disclosure does not in any way endorse or encourage the unnecessary withholding of any material relevant to a case.
"It is, however, right that in cases involving sensitive unused material, such as details of an informant, that this is not automatically shared with the defence.
"This is entirely in line with legislation and national guidelines and is well understood by defence and prosecution alike.
“At the same time, we know that investigators need more effective, consistent training and advice so they have absolute clarity about the disclosure process - and this is central to the improvement plan we have put into action with the Crown Prosecution Service (CPS) and College of Policing.”