Consent forms, which ask permission to access messages, photographs, emails and social media accounts, have been rolled out across the 43 forces in England and Wales.
The move is part of the response to the disclosure scandal, which rocked confidence in the criminal justice system when a string of rape and serious sexual assault cases collapsed after crucial evidence emerged at the last minute.
Police and prosecutors say the forms are an attempt to plug a gap in the law, which cannot force complainants or witnesses to disclose their phones, laptops, tablets and smart watches.
But, Northumbria Police and Crime Commissioner Dame Vera Baird said the forms are just part of the problem as police and prosecutors look to harvest third party material, such as school records and medical notes.
“The police are really saying, ‘if you don’t let us do this, the CPS won’t prosecute,’” she said.
“It is a real concern that people will be put off making a complaint in the first place if it’s widely thought they are going to have to hand over lots of personal data - everyone lives on their phones, particularly teenagers.”
In the lead-up to trials, police and prosecutors are required to hand over relevant material that can undermine the prosecution case or assist the defence.
The regime came under sharp focus from the end of 2017 after a string of defendants, including student Liam Allan, then 22, had charges of rape and serious sexual assault against them dropped when critical material emerged as they went on trial.
The CPS launched a review of every live rape and serious sexual assault prosecution in England and Wales and, along with police, has implemented an improvement plan to try to fix failings in the system.
Some 93,000 officers have undertaken training, while police hope artificial intelligence technology can help trawl through the massive amounts of data stored on phones and other devices.
The new digital consent forms can be used for complainants in any criminal investigations but are most likely to be used in rape and sexual assault cases, where complainants often know the suspect.
Police and prosecutors have sought to reassure victims of crime that only material relevant to a potential prosecution will be harvested, but the forms state even information of a separate criminal offence “may be retained and investigated”.
Privacy campaign group Big Brother Watch said “treating rape victims like suspects” could deter people from reporting crimes.
The Information Commissioner’s Office said it has launched an investigation into use of data extraction technology on the mobile phones of suspects, victims and witnesses.
A spokeswoman said: “We are also currently looking at concerns raised around the collection, secure handling and the use of serious sexual crime victims’ personal information.
“A separate investigation will be tracking the journey victims’ information takes through the criminal justice system, from allegation, through disclosure and on to any compensation application that may be made.
“This is to identify areas where victims’ information is most vulnerable or where processing may be excessive and disproportionate.”