Her Majesty's Inspectorate of Constabulary, which independently assesses policing in England and Wales, found the police had "some way to go".
Only three of the 43 forces in England and Wales were "prepared to some extent" in protecting and supporting victims effectively, while "every police force must improve its understanding" of the problem.
The publication, entitled "The Depths of Dishonour: Hidden Voices and Shameful Crimes", also shone a light on the scale of the problem, fearing those victims who come forward are just the tip of the iceberg.
"They are assaulted and betrayed by the people closest to them, their family and community, from whom they have the right to expect love and protection.
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Studies show FGM is chiefly rooted in Britain's African communities, while forced marriage is largely found in its South Asian communities.
The report cited research which found more than 11,000 HBV cases, including domestic abuse and rapes, were recorded by police forces between 2010 and 2014, though "the scale of the problem remained unknown".
Of the 1,267 cases handled by the government's Forced Marriage Unit in 2014, 38 per cent related to Pakistan, eight per cent to India and seven per cent to Bangladesh.
Government figures indicate that tens of thousands of women in Britain are living with the consequences of FGM.
"The hidden nature of these crimes means that it is likely that, of the victims who come forward, there are many more who haven't," said Inspector of Constabulary Wendy Williams.
One victim interviewed for the report said police were "too scared of coming across as racist".
"They need a dedicated team, who really understand the different cultures. And they need to talk to victims and survivors" more than being "educated by books" on the issues, the interviewee said.
Chief Inspector of Constabulary Thomas Winsor said victims felt hopeless and helpless.