Victims of rape face a "postcode lottery" in the way they are treated, according to a report published on Friday.
The women's equality group, the Fawcett Society, is calling for more specialist centres dealing with sexual assaults to be set up.
It comes a day after the latest crime figures showed reported rapes up by 27% in a year, although the Home Office said this was in part due to new methods in recording crime.
The Labour MP Vera Baird, who chairs the Fawcett Society, said support for victims was "patchy".
She said the best was offered in areas with a Sexual Assault Referral Centre, and there were just seven of those around the country.
These offered a "gold standard" of care, she said, and at least 12 more were needed.
The alternative, she said, was that a victim rang a bell at the reception desk of their local police station, and had to "say in an open waiting room, 'I've been raped'".
"You take you chance about which kind of officer comes to you, whether that person has any expertise or is a man or a woman," she told BBC Radio Five Live.
"And then, if you're referred to a detective, you take your chance again as to whether that detective has any relevant expertise."
She said the ordeal continues, as the a forensic medical examiner is called, which can take hours and could be of either sex.
More Sexual Assault Referral Centres
24-hour rape crisis helpline
Allocation of specialist police officer from start to finish of case
Home Office figures suggest 5% of women had been raped since the age of 16,
although a 1991 survey indicated the figure for rape or attempted rape may be as
high as 25%.
The society is calling on the Home Office to direct more resources to the areas without these specialist centres and "galvanise" police forces and health trusts to contribute better to the victim's experience.
The society praised government attempts to make the prosecution process easier for victims.
However Ms Baird added: "There's no point changing the law about trial if you can't get women to go to court."
A Home Office spokesman said:
"We will shortly be publishing a Victims and Witnesses strategy which will
set out further ways in which we are putting victims at the heart of the system,
giving them more of a voice, and ensuring they see justice done more often and
"During the Commons debate on the Sex Offences Bill the home secretary
confirmed the government's intention to set up a rape helpline.
"This is one of
the issues that will be taken forward by the new cross-government ministerial
group on sexual offending."