Rape complainants are preparing to take legal action against police chiefs over requests to disclose sensitive digital records in order to proceed with rape investigations. Victims and specialists say the practices are disproportionate and may deter victims from reporting sexual assaults.

New consent forms formalise how police forces can ask for historical data including photos, texts and emails from phones, laptops and other digital devices or complainants risk having their cases dropped.

On Monday Maria Miller, the Conservative MP who chairs the cross-party women and equalities committee, warned the forms could “undermine” victims’ access to justice. The Labour leader, Jeremy Corbyn, also criticised the increased disclosure “with rape and sexual assaults already under-reported, this disturbing move risks letting more rapists get away with it”.

One of the claimants taking legal action against the police, who says she was attacked by a group of strangers after being drugged, said: “This isn’t about trying to stop the police from putting together the facts of the case. This isn’t about objecting to the police downloading information from the time that it happened. This is about objecting to the police downloading seven years of information that pre-dates the event and therefore has zero relevance.”

Another claimant said: “I’m extremely concerned about the data on my phone being handed to my attacker as part of disclosure. Nobody would want their mother to look at their phone. Nobody would want their employer to know what they are searching, or to see their photos. Now imagine your rapist gets access to that.”

Kate Ellis, a solicitor at the Centre for Women’s Justice, said the CPS seemed to be increasingly reluctant to bring charges in rape cases which were based on one person’s word against another – which she said was the case with the majority of rape allegations.

“The police and the CPS need to be careful that they are striking the right balance, between protecting suspects – the right to have proper disclosure if the case goes to trial and the right to be protected from a misguided prosecution – and the very significant public interest in bringing serious sex offenders to justice,” she said. “I’m just worried that the effect will be that complainants will be deterred from coming forward.”

The consent form follows reporting by the Guardian revealing a patchwork approach to disclosure requirements for rape complainants across the country, as people in different police force areas may be asked to grant access to a wide range of personal records.

In London, the Metropolitan police can request access to social media, web browsing activity and content, instant messages, location data, emails, deleted data, images, videos, audio files, apps, contacts, documents, MMS and SMS messages – which can be kept for up to 100 years.

The new disclosure forms only deal with digital evidence. However, a large amount of non-digital evidence can also be asked of complainants.

According to forms released to the Guardian under the Freedom of Information Act a rape complainant in Merseyside can be asked to sign a form granting police access to any personal medical and counselling notes, educational notes, social services records and “any other personal confidential records of mine that they [police] feel may be important”. The information may be then disclosed to the CPS, the defence and discussed or used as evidence in court.

Rachel Krys of the End Violence Against Women Coalition said that victims need to have representation, ideally by lawyers, at police stations when they make initial complaints of sexual assault.

“People don’t know their rights,” she said. “They are being expected to sign these forms just at the time they have been through a really horrible experience. There ought to be a lawyer or a specialist there to help them. It should be properly resourced and paid for by the state.

“Victims don’t understand how broad the requests will be. This concern about disclosure is forcing people to hand over information much earlier.”

Katie Russell, national spokesperson of Rape Crisis England and Wales, said it felt that the pendulum had suddenly swung back to doubting the victim. The new police form, she said, was “heavy with jargon and deeply problematic”.

She added: “It’s problematic calling this a consent form when the victim is not being given a choice. It’s either sign away [the contents of your phone] or your case will not be investigated.

Disclosure requirements are under investigation by the Information Commissioner’s Office as to what information is asked of victims at the time of reporting serious sexual crimes.

Vera Baird, the Association of Police and Crime Commissioners (APCC) victims lead, said: “It’s bound to rub up against privacy rights. The problem is that by opening up what is searched to way beyond the relevant, you are likely to come across things that can be used to discredit the complainant about completely unrelated matters. The police and CPS will be unable not to disclose the information and this is only done in rape and sex offence cases.”

Rape prosecutions fell to a five-year low in the six months to September 2018, as just over a third of cases brought to the CPS.

A CPS spokesperson said: “Sexual offences can have a devastating impact and it’s important that victims have confidence that if they report a crime, it will be handled sensitively and fairly by police and prosecutors...”

“Searches of mobile phones and social media are not automatic, and only information that is relevant to the case may be assessed. Guidance to police and prosecutors is explicit that only reasonable lines of inquiry are pursued, to avoid unnecessary intrusion into a complainant’s personal life.”