People with severe mental illness are "significantly more likely" than the general population to report that the police have been unfair or disrespectful, new research has shown.
Many people with mental health problems told a UK survey they were not being believed when they attempted to report a crime or seek help.
And many were reluctant to report crimes to police or other professionals, saying they feared their illness would be used to discredit them or they would be sectioned, the study by charities and academics found.
Charity Victim Support, the Institute of Psychiatry at King's College London, Mind, the mental health charity, the Faculty of Health, Social Care and Education at Kingston University and St George's, University of London, in collaboration with University College London, completed the research.
Mind's chief executive Paul Farmer said: " People with mental health problems have an equal right to justice, yet this report reveals that this is not the reality for far too many of us.
"It is unacceptable that the police, healthcare staff and others who are supposed to support victims of crime may be dismissive of or not believe a person's experience, or may even blame them for the crime.
"We are calling on the police, commissioners, healthcare staff, support agencies, local and national government to work together and improve services for people with mental health problems who are the victims of crime."
Elsewhere, the report found people with severe mental illness were three times more likely to be a victim of any crime and five times more likely to experience assault.
Women with severe mental illness were 10 times more likely to experience assault.
Nearly 45% of people with severe mental illness reported experiencing crime in the last year, while 62% of women with severe mental illness reported being victims of sexual violence as adults.
Authors of the report - titled 'At risk, yet dismissed: the criminal victimisation of people with mental health problems' - called for an urgent national debate across Government on how to respond to the needs of victims of crime with mental health problems.
Victim Support chief executive Javed Khan said: " It is nothing short of a national scandal that some of the most vulnerable people in our society become victims of crime so often and yet when they seek help they are met with disbelief or even blame.
"It is unacceptable that the criminal justice system fails to meet the needs of people with mental health problems when this report shows all too clearly the terrible impact of crime on them."
The three year study was funded by The Big Lottery Fund and interviewed a random sample of 361 people with severe mental illness in London.
Commander Christine Jones, the lead on mental health for the Association of Chief Police Officers (Acpo), said: "Anyone reporting a crime against them expects to be listened to, taken seriously and treated with respect.
"They also expect appropriate action to be taken to investigate their case and to be signposted to further support if they need it.
"We want to ensure that people with mental ill health get that same, high quality service from the police if they have been a victim of crime."
She added: " Acpo and the College of Policing are already working with colleagues in government, health, social care, commissioners and mental health charities to identify opportunities to improve services, share information and better understand the needs of people with mental ill health. We support the recommendations in this report, which will further that work."