Two thirds of rape cases in Lancashire are closed by police because of problems with evidence.
The Home Office data – which also shows that just one in 17 cases ends with anyone being charged – reflects the difficulty police face in bringing suspects to court.
This week, it was revealed that rape victims are being told they must hand over their mobile phones to police or risk prosecutions against their attackers not going ahead.
Between January and September 2018, 1,079 rape investigations were concluded by Lancashire Constabulary.
Just 64, or six per cent, of them resulted in a suspect being charged.
Lancashire was the only police force in England and Wales not to provide crime data for the final quarter of 2018.
The most common reason for rape investigations being closed was evidential difficulties, and even though a named suspect had been identified the victim did not support police action, or withdrew support from it. This accounted for 33 per cent of cases.
In a further 23 per cent, a suspect had been identified and the victim supported police action, but evidential difficulties prevented the case proceeding.
In nine per cent, the crime was confirmed by police, but no suspect was identified and the victim declined or was unable to support further police action.
Another 21 per cent of cases were closed with police concluding that the crime had been investigated as far as reasonably possible, pending further avenues of interest opening up.
Recently, consent forms asking rape victims for permission to access their messages, photographs, emails and social media accounts have been rolled out across the 43 forces in England and Wales.
Max Hill, the Director of Public Prosecutions, said digital devices will only be looked at when it forms a "reasonable line of enquiry" and only "relevant" material will go before a court if it meets "hard and fast" rules.
"If there's material on a device, let's say a mobile phone, which forms a reasonable line of enquiry, but doesn't undermine the prosecution case and doesn't support any known defence case, then it won't be disclosed," he said.
But the policy faced an immediate backlash, with the End Violence Against Women Coalition saying the forms reinforced "prejudices and barriers" against rape victims.
Rachel Krys, co-director of the coalition, said: "We have an extremely serious problem with prosecuting rape in this country and it is a fact that most rapists get away with it.
"Part of the reason for this is that investigations too often focus on women's character, honesty and sexual history, despite rules which are supposed to prevent this, instead of the actions and behaviour of the person accused.
"There is no reason for rape investigations to require such an invasion of women's privacy as a matter of routine."