The percentage of reported rapes to lead to convictions in England and Wales has fallen to an all-time low, according to a Home Office study.
More women are coming forward to report rapes
The number of rapes reported is rising - but only 5.6% of 11,766 reports in 2002 led to a rapist being convicted.
Researchers tracking 3,500 court cases found "sceptical" prosecutors and police often did not believe victims.
There was also "some evidence of poor investigation and understanding of the law", they added.
Of the 11,766 allegations of rape made in 2002 there were just 655 convictions, 258 of which had come from a guilty plea. Only 14% of cases pursued made it to trial.
The report, carried out at London Metropolitan University, said crime data suggested up to 47,000 rapes were actually committed every year.
'Culture of respect'
The proportion of convictions had dropped to 5.6% from 6% the previous year.
The government had promised to address the "justice gap", said the report, but there first needed to be a shift in the criminal justice system from a focus on the ability to discredit complainants to improved evidence-gathering.
"Data on reported rape cases... show a continuing and unbroken increase in reporting to the police over the past two decades but a relatively static number of convictions, thus the increasing justice gap."
Rape was a unique crime because in no other cases were victims subjected to such scrutiny in court, the study - called A Gap or a Chasm? - said.
Defendants were also far more likely in rape case to claim the victim consented to the alleged attack, it added.
Researchers said if the government was to improve results there should be a "culture of belief, support and respect" among those involved in dealing with rape allegations.
An overestimation of the scale of false allegations among some officials led to victims losing confidence in the system , said the authors at the university's child and woman abuse studies unit.
There should also be more female staff available to deal with victims, and more information for victims and "courtroom advocacy that does justice to the complainant's account".