Police often advise women to drop their complaints
Professor Liz Kelly, who is leading a Home Office study into the issue, says there are wide variations in the way police deal with rape complaints.
Initial findings of the study indicate that some officers act unprofessionally, while others encourage women to drop their allegations.
Prof Kelly said examples of excellent work were outnumbered by bad or indifferent practice, with many investigations "falling apart" when detectives became involved.
Prof Kelly told the BBC she thought there were "layers of problems" with the way the subject was dealt with.
"There are some pockets of really excellent, wonderful work, but in the main it's a lottery and if you don't live near one of those areas then you may get not very good practice or even bad practice.
"There are police officers who work with these old fashioned stereotypical ideas and if women fall into one of the categories they don't respect, then they're not very good at handling that encounter."
Timing
She had encountered cases where police were rude to victims, made sexist comments or suggested they drop their complaints.
In one example, police officers talked with a doctor about their holidays as he carried out an internal examination on a victim.
Prof Kelly, who teaches children and women abuse studies at the University of North London, said she had found some officers overlooked the importance of timing in dealing with victims.
"It's not appropriate within hours or days of reporting a rape to be telling someone how hard it is to take it through court," she said.
"The police think they are being open and honest, but the perception by the victim is often that they're telling them they shouldn't bother to continue."
The report, currently at its half-way stage, is likely to recommend the setting up of more self-referral centres, where women can report rapes without initial police involvement.
It is also expected to call for the use of specialist rape teams to conduct investigations.