Failure to disclose vital evidence is the biggest single cause of miscarriages of justice and the problem is getting worse, the outgoing chairman of the Criminal Cases Review Commission (CCRC) has said.

Richard Foster also highlighted a shortage of adequately trained investigators, resulting in criminals escaping justice, “trials collapsing at the courtroom door” and “convictions which prove unsafe” and are avoidable.

Foster, a former chief executive of the Crown Prosecution Service, said he was “disappointed and concerned” the CPS and police declined to conduct a targeted review of past convictions to expose the extent of disclosure problems.

“If the state gets it wrong, it is the state’s responsibility to put things right. The CCRC has been in touch with the law officers and the CPS to propose such a review and to offer to assist,” he said.

“That offer has not been taken up. In my view, there is a risk that serious miscarriages of justice will go undetected and unrectified as a result.”

Foster, who has chaired the CCRC for the past decade and whose grandfather was a police officer, said the number of unsafe convictions in the criminal justice system was unknown and its processes had “systemic weaknesses”.

In an annual report five years ago, he said, he had pointed to disclosure failures as the “continuing biggest single cause of miscarriages of justice”.

Asked about disclosure problems and the volume of material produced by digital media, Foster said: “I think it’s getting worse. I think particularly in rape, where it turns on who you believe. Social media media data is of the essence.”

An emergency CPS review of live cases earlier this year led to 47 being dropped on non-disclosure grounds. The service said many of those cases might eventually have been stopped.

But Foster said: “Even if true, this ‘well we would almost certainly have got round to dropping the cases in the end’ defence is scant comfort to those who will have had to suffer months if not years of unnecessary uncertainty and opprobrium.

“I do not myself think that the CPS contention that the existing checks and balances in the system guarantee cases which should be stopped will always be stopped before trial is supported by current evidence.”

A combination of technological challenges and funding cuts is putting huge pressure on the criminal justice system, he said, while there appeared to be a lack of experienced investigators within the police.

In a recent investigation into a gang killing, Foster said the CCRC had to look at “potential wrongdoing by senior police officers”. To conduct the inquiry, a senior police officer was recruited.

“I was taken aback when I talked to HM Inspectorate of Constabulary and discovered how few of the 43 chief constables had recent strong, investigative backgrounds,” he said.

The recent CPS review of live cases “points to instances where lines of inquiry which might have stopped the case in its tracks had simply not been identified by investigators at all, or if identified, not followed up”, he added.

Recalling a historical case, Foster said: “Mahmood Hussein Mattan was hanged on 3 September 1952 for the murder of Lily Volpert. His conviction was among [the CCRC’s] very first referrals. Vital evidence was simply not disclosed by the police.

“In quashing the conviction, the court of appeal stopped short of saying that an innocent man had been hanged, though that is obviously what happened.

“We no longer hang people … [but] even today, we all too often still see instances where the investigation and preparation of criminal prosecutions fall well short of the highest standards of integrity, conscientious and professional skill.”

A CPS spokesperson said: “We keep prosecutions under review throughout the life of the case. This means as they develop and progress, they can quite rightly be stopped at any time.

“In our recent review, we analysed why cases were halted and found nothing to suggest they would not have been stopped by the checks and balances built into the system. This is why we do not think a broader review is appropriate.”