Evidence is being hidden and deliberately withheld in a "very worrying" failure of disclosure by police and prosecutors, a Freedom of Information request has suggested.
Documents obtained by the Centre for Criminal Appeals (CCA) reveal a significant and "perennial" problem with the repeated view that defence teams are not entitled to see all the evidence.
The findings come on the heels of a string of cases abandoned at the 11th hour due to late disclosure of evidence.
The charity asked the Crown Prosecution Service Inspectorate for more than a dozen 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 - 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.
David Tucker, from the College of Policing, said it provided no training or guidance to officers encouraging them to withhold evidence.
He said: "Since last summer, police and the Crown Prosecution Service have been working to address the criticisms identified in a joint Inspectorate report into disclosure.
"In January those at the highest levels of both organisations committed to a joint action plan which is now moving at a considerable pace to start to bring the necessary change."
The CCA said it is challenging a refusal to disclose which police force the notes refer to.
Suzanne Gower, solicitor and CCA managing director, said it was "unrealistic" to expect the mindset on disclosure to change.
She said: "These documents show why responsibility for providing full and fair disclosure must be taken out of the hands of police and prosecutors.
"The truth is they see themselves first and foremost as adversaries to the defence and, in some cases, deliberately withhold exculpatory evidence."
The charity is calling for an independent disclosure agency to be established, which they hope would prevent wrongful convictions.
In December, two rape cases collapsed, sparking an urgent review by Scotland Yard into every one of its sex crime investigations where a suspect has been charged.
The trial of Liam Allan, 22, was halted at Croydon Crown Court on December 14, and the prosecution of Isaac Itiary, accused of raping a child, collapsed a few days later.
In January, the case against Samson Makele, 28, was halted at Snaresbrook Crown Court after his defence team unearthed key images from his mobile phone which had not previously been made available, law firm Hodge Jones and Allen said.
A BBC investigation found that more than 900 criminal cases were dropped last year due to a failure by police or prosecutors to disclose evidence.