By Sue Littlemore
Social affairs correspondent, BBC News
The Equality Commission has conducted research into provision
More than 100 councils could face legal action for not providing specialist support services for women affected by sexual violence.
Every year three million women in Britain become victims of rape or other forms of sexual abuse.
The Equality and Human Rights Commission says councils have a legal duty to provide support for victims and is threatening court action.
The Local Government Association said the threats were "irresponsible".
Research published by the Equality Commission and the End Violence Against Women Campaign suggests there is a major funding gap for facilities such as rape crisis centres which help women escape violence and abuse.
The study, called the "Map of Gaps," charts services across Britain and suggests more than 100 local authorities, a quarter of the total, have no specialised help at all.
The worst provision per head of population is in the east and south east of England and the best provision is in Bradford.
But the research found Glasgow had the best provision in the whole of Britain because women's safety had been made a priority there.
Chair of the Equality Commission, Trevor Phillips, is writing to the areas where there are no services to say unless they have a good explanation he will take legal action.
He said: "In many parts of the country services for women who have experienced violence are chronically under-funded or simply do not exist.
"Women shouldn't be subjected to this postcode lottery... for those councils who continue to ignore the dire need to shore up services and plug the gaps we have a stark reminder: the commission is ready and willing to use its enforcement powers."
The Local Government Association described the study as "irresponsible and alarmist".
Cllr Ann Lucas, LGA spokeswoman on domestic violence, said women and men who experienced violence did not just get help and support from councils.
"Councils work with other organisations like the police, the health service and voluntary organisations in order to make sure women get the support they need, when they need it," she said.
"There is a responsibility on councils to consider what services are needed in their area to support women and men who experience violence. If the council decides there are enough existing services being provided by other organisations, they won't provide a service just for the sake of it.
"Writing a letter to 100 councils asking why they have no specialised services and pursuing them in the courts will be of no help to anybody."
In addition to the threat of legal action, the Commission is launching an online interactive "Map of Gaps," which enables the public to find out about provision in their area and lobby their MP and local authorities to press for more investment in these vital services.