The Crown Prosecution Service has come under fire for waiting nearly a year and a half to charge a man accused of raping a 12-year-old boy despite him admitting to the crime.

The child and his family were devastated by the lengthy delay as the CPS insisted on trawling through 40,000 files of the victim’s personal data.

The lawyers representing the boy have lodged a complaint, seen by the Guardian, to the Information Commissioner’s Office (ICO), as part of the watchdog’s ongoing enquiry into the collection, analysis and disclosures of complainants of sexual offences’ personal information and digital data.

They are calling for updated national guidance on police and CPS access to digital data, particularly digital data that belongs to complainants of sexual offences.

The perpetrator, 30, handed himself in to the police in January 2017 and admitted to officers he had been having sex with a minor and had potentially given him an sexually transmitted infection. In or around February 2017, the victim was identified and confirmed what had happened.

The perpetrator, who went on to plead guilty to rape, attempted rape and sexual touching of a child under 13 at trial, was not charged by the CPS until July 2018. He was convicted in September 2018.

Lawyers from Bindmans LLP, who are representing the victim, said the Metropolitan police had repeatedly informed them that the delay in charging was due to the CPS’s request that officers obtain and review the victim’s electronic data in their possession, which included 40,000 digital files on the child’s phone.

The complaint states the victim was left in limbo for several months as the CPS insisted on an extensive electronic review of his personal data before a charging decision, but police officers said they prioritised reviews of electronic data only in cases where a charge has been made.

The complaint comes amid growing concern that police forces across the country are demanding highly personal records and data – including health, school and college records, and counselling notes – from potential rape victims before pressing ahead with their cases. Campaigners have long warned that victims will be put off going to the police by the intrusion into their lives.

Rachel Harger, a solicitor at Bindmans who is representing the client, said there was no updated national guidance on police and CPS access to digital data, particularly on digital data that belongs to complainants of sexual offences rather than suspects.

She said: “In turn, there were no existing effective safeguards which would and should have protected my client against the overly intrusive, overly broad and irrelevant requests for his digital data, which was then unnecessarily reviewed prior to a charging decision being made. We have seen absolutely no evidence as to how any of this digital data contributed to the CPS’s charging decision or the conviction of the perpetrator.

“Furthermore, this intrusive conduct obstructed my client’s ability to obtain some form of justice and it led to an entirely disproportionate delay particularly when taking into account the nature of the admitted offence and his vulnerability as a child.”

Griff Ferris, a legal and policy officer at Big Brother Watch, said: “This shocking case exposes the Crown Prosecution Service’s blind insistence on investigating rape victims’ irrelevant digital information. It’s disgraceful that, despite the rapist admitting to his crime, the CPS still wanted to investigate the 12-year-old victim’s phone and private life. Treating rape victims like suspects delays investigations and trials, deters victims from reporting and ultimately obstructs justice.”

An ICO spokesperson said it would not comment on individual complaints, but commented: “The ICO has an ongoing investigation into the use of data extraction technology on the mobile phones of suspects, victims and witnesses.

“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.”

A CPS spokesperson said: “We will consider the matter carefully and respond in due course.”

A Metropolitan police spokesperson said: “In September 2017, the Met received a complaint relating to an investigation into the rape of a child. The matter has been temporarily stayed. It would be inappropriate to comment further at this time.”