Police are regularly withholding critical evidence in criminal cases where it might undermine their case, and some officers are ‘trained’ in the technique, which could be leading to miscarriages of justice.

The revelation comes after police and the Crown Prosecution Service (CPS) were accused of deliberately trying to drive up conviction rates for certain crimes, and London police were forced to review all pending rape cases because of failures.

Over the past six months, a number of high profile rape cases have collapsed, after critical evidence proving the innocence of accused men was withheld from defence teams.

England’s Top Prosecutor Stepping Down After ‘Guilty Until Proven Innocent’ Rape Trials https://t.co/lhPpUqKF4n — Breitbart London (@BreitbartLondon) April 3, 2018

Now a dossier, seen by The Times and drawing on reports from 14 focus groups with police, shows why this may be. It was compiled by the Centre for Criminal Appeals, and also uses reports from focus groups with prosecutors and judges and a survey of prosecutors.

In it, authorities are accused of deliberately withholding important information for too long and failing to record statements from witnesses not helping the prosecution.

The revelations come after CPS boss Alison Saunders’ announcement she will be stepping down after heavy criticism. In her time in charge, she promised to pursue “online hate crimes” rather than some physical crimes, and police have been told to “believe” all rape claims regardless of evidence.

Comments recorded in the dossier include police saying: “If you don’t want the defence to see it, then [evidence] goes on the MG6D,” in reference a list of material to which is withheld from the defence.

Police Chief: ‘Automatic Belief’ of Rape Accusers Needs Review, Restore ‘Innocent Until Proven Guilty’ https://t.co/JR5uYeoTrS — Breitbart London (@BreitbartLondon) December 21, 2017

One prosecutor blasted: “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.”

An inspector also noted that police “have been trained to put items on there that they do not want disclosed to the defence”. This tactic was confirmed by prosecutors. One recorded comment was that “officers put undermining material on the MG6D list to hide”.

In one report on focus groups with judges, the inspectors note a judge saying: “There seems to be an idea that the defence is not entitled to see things but where the defence press matters, this yields results.”

In December last year, a rape case against Isaac Itiary was thrown out when it emerged that the 15-year-old accuser had insisted she was 19.

Days earlier, the case against student Liam Allan, 22, also collapsed in similar circumstances when lawyers were handed messages which showed the complainant had enjoyed sex with him.

In the same month, another man, Danny Kay, 26, had a conviction quashed after spending four years in jail because police did not thoroughly investigate Facebook messages.