Victims of rape and domestic violence have no crisis centres or refuges to go to in some parts of Britain.
There is a 'postcode lottery' in provision, with some areas reasonably well served, and others having no services at all, says the Commission for Equality and Human Rights and the coalition End Violence Against Women (EVAW).
The Commission's chairman, Trevor Phillips, said the organisation may take legal action in a year's time under gender equality legislation to ensure women have access to services.
The Commission and EVAW's report, Map of Gaps, shows how provision varies across the country.
Five areas are particularly underserved, the organisations said - the east of England, London, Northern Ireland, the north west and the south east.
While very few areas could claim to have sufficient provision to meet the needs of women who had recently suffered violence, the nine with the most extensive services were: Birmingham, Bradford, Glasgow, Hammersmith & Fulham, Leicester, Liverpool, Manchester, Nottingham and Sheffield.
In Scotland the situation was more positive, the organisations said.
A spokeswoman said of the situation there: "There is a commitment to funding for specialised services. This means that services are distributed more equally and there has been an expansion in rape crisis centre provision."
Mr Phillips said there was "an undeclared war against women in this country".
Each year, some three million would experience violence in one form or another. In a fair Britain, he said, every woman should have someone to call in a crisis, access to a place of safety, genuine backing in her search for justice, and should be treated fairly and sympathetically by the criminal justice system.
