Police continue to provide a "patchy" service when they investigate rapes, a review of their progress has suggested.
Fewer than 6% of reported rapes resulted in a conviction
The Association of Chief Police Officers' working group found fewer than 10 forces in England and Wales had dedicated rape investigation teams.
It also found some were not gathering forensic evidence quickly enough.
The review was carried out three years after police were given new guidance on investigating rape, to try to increase the number of successful prosecutions.
Only about 6% of reported rapes result in a conviction.
The progress report found that a number of forces - including the Metropolitan Police, Derbyshire and Greater Manchester - had made significant improvements.
But eight forces were not using early evidence kits, which allow samples to be taken at the scene.
Deputy Assistant Commissioner John Yates, who conducted the review, said it was "best practice" to have dedicated teams though it might not be possible in smaller forces.
Mr Yates said between 80% and 90% rapes went unreported, which meant police had a "substantial intelligence gap" as they could not assess the true pattern of offending.
Mr Yates is the head of the Association of Chief Police Officers' working group on rape.
Ruth Hall from support group Women Against Rape said that, while some officers really did want to get convictions, Mr Yates' report showed that rape cases were not a priority for police as a whole.
"The police are often very careless when handling evidence, they lose evidence, or they don't recognise evidence when it's put in front of their faces or they misinterpret facts," she said.
Ms Hall welcomed the fact the report had been carried out but warned that similar calls for improvements in the past had failed to get results.