Two out of three gay, lesbian and bisexual people are likely to have mental health problems - compared to just one-third of heterosexuals, according to the largest study of its kind in the UK.

Nearly a third of gay men and more than 40 per cent of lesbians, who are open about their sexuality, also reported prejudice from mental health workers, the study reveals.

The findings will be published this week in a report by Mind, the mental health charity, launched at a conference about the mental health needs of gay men, lesbians and bisexuals. Researchers at University College London (UCL) interviewed 2,400 gay men, lesbians, bisexuals and heterosexuals in a three-year study financed by the Community Fund. The Independent on Sunday has been campaigning for more than a year for better services for people with mental health problems.

Until 1992, homosexuality was classified as a mental disorder by the World Health Organisation. Existing research from US experts shows that gay people have much higher rates of depression and suicidal behaviour because of intolerant attitudes towards their sexuality.

This is backed up by the UCL report, which shows prejudice is rife among doctors and psychiatrists.

For example, 61 per cent of bisexual women and 42 per cent of lesbians encountered a hostile response from medics. This ranged from overt homophobia and discrimination to a perceived lack of empathy by the clinician. Many of those interviewed for the UCL study said they wanted to be able to choose a lesbian, gay or bisexual clinician.

The study authors recommend that the Government provide guidance on preventing self-harm for lesbian, gay and bisexual people and that doctors should strike a balance on how they treat gay people.

Louise, 21, whose name has been changed to protect her identity, was offered treatment for "going straight" by her doctor when she said she was a lesbian. The web-designer has suffered depression and used to self-harm, a direct result of the stigma of her sexuality. "I was 13 and I told the doctor ... it [was] hard to cope with my sexuality, that I needed to talk to someone," said Louise, who lives with her parents and 17-year-old girlfriend in Huddersfield, West Yorkshire. "He told me that there were clinics ... for going straight. I went home and harmed myself." At the age of seven, Louise had realised she was sexually attracted to women but did not "come out" until her teens.

She still feels unable to hold her girlfriend's hand in public because of the verbal abuse she receives from groups of men. In her opinion, doctors should be asked about their attitudes towards gay and lesbian people, and need more training.

"Your sexuality is up to you," Louise said. "My partner won't see a male doctor because she is frightened of their opinion. We need more 'gay-friendly' doctors."

Mind said that clinicians needed more training so they could offer proper support to people who self-harmed or were suicidal because of their attraction to the same sex.

Sophie Corlett, Mind's policy director, said: "Mental health professionals clearly need more training in order to empathise with ... their gay, lesbian and bisexual service users and offer them appropriate services."