Evidence has been withheld from lawyers in 47 rape and serious sexual offence cases, a Crown Prosecution Service (CPS) review has found.
The figure follows a national review launched after several rape cases collapsed when it emerged police and prosecutors failed to pass vital information on to defence lawyers.
Director of Public Prosecutions Alison Saunders said: "Getting disclosure right is a fundamental part of a fair criminal justice system. Our analysis shows that in the vast majority of cases we are doing that.
"But there are cases where we are falling short – and that is unacceptable. I recognise the huge impact on individuals involved, and deeply regret every case where mistakes have been made.
"My priority, working closely with the police, is to put in place effective measures that bring about a sea-change in how disclosure is managed so that complainants and suspects alike can have confidence that every case is fair."
The CPS revealed on Tuesday that there had been issues with disclosure in 47 of the 3,637 cases in England and Wales, which were reviewed earlier this year.
In five of the cases, disclosure was the main reason why the case had to be stopped. In the remaining 42 cases, reasons such as text messages, emails and social media being examined too late were cited.
The failure to retrieve medical or social services records or new evidence emerging after the initial charge were also noted in the review.
Fourteen defendants were in custody when the decision was made to stop their cases.
"We've got to realise that this is about real people," said Assistant Chief Constable Stuart Prior, disclosure lead for the National Police Chiefs Council (NPCC).
"Whether that is a person reporting a matter to us, whether it be a person as a witness, or whether it be somebody accused of an offence. That's incredibly traumatic, whatever aspect you look at.
"We've got to get disclosure right. We cannot allow mistakes to impact so greatly on people's lives as has been played out in the media over the past few months.
"Our whole criminal justice system is based on fairness – fairness of investigations, fair trials and we have to strive and provide that for all the people who come into the criminal justice system. We have got it wrong in too many cases."
CPS legal services director Gregor McGill did not say if any lawyers would face disciplinary action over the halted cases and as for police, Mr Prior said it would be a matter for individual forces.
When asked about potential compensation claims, Mr McGill added: "Just because a case has been stopped doesn't necessarily mean that anyone is at fault."
On Tuesday, Ms Saunders, the College of Policing's chief executive Mike Cunningham and the NPCC's Chief Constable Nick Ephgrave are to give evidence to the Commons justice select committee.
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It comes as new measures are being introduced, including training for prosecutors and police officers and measures to deal with disclosure earlier in the legal process.
There are also plans for improved technology to help investigators work through large amounts of communications data.
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