Attempts to change a person’s sexual orientation result in high levels of mental health problems including suicide attempts, self-harm and eating disorders, according to a survey.

Some respondents said they had been forced to undergo “conversion therapy”, and a handful said they had been compelled to take part in sexual activity with someone of the opposite gender.

The survey on faith and sexuality, conducted by the Ozanne Foundation, which campaigns for LGBT+ equality, will be presented to members of the Church of England’s synod, the C of E governing body, which is meeting in London this week.

The results were “shocking and sobering”, said Paul Bayes, the bishop of Liverpool and the foundation’s chair. “The statistics reflect lives which have been scarred and strained by mixed messaging of love, acceptance, condemnation and fear.”

In July 2017, the C of E condemned the practice of conversion therapy, which aims to change sexual orientation, as unethical and potentially harmful, and called on the government to ban it. It had “no place in the modern world”, said a motion passed overwhelmingly by synod members.

However, a few Anglican churches and others in the Pentecostal tradition still encourage people to take part in prayer sessions or “deliverance ministry” to change their sexual orientation.

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Out of more than 4,600 people who took part in the online faith and sexuality survey, about 10% – 458 – said they had undergone efforts to change their sexuality. Of those, almost one in 10 said they had been “given no choice” in the matter and 22 people said they had undergone forced sexual activity with or involving someone of the opposite gender.

The most common reason given was a belief that their desires were “sinful”. About half were teenagers at the time; a few said they had been under the age of 12. More than three-quarters said the attempt to change their sexual orientation had not worked. Thirteen people said it had “worked completely”.

Over half reported mental health problems, most commonly anxiety and depression. Almost 300 people said they had attempted suicide or had suicidal thoughts. More than 100 said they had self-harmed and 70 reported suffering from eating disorders.

Bayes said: “It’s clear there is a whole lot of hurt that the churches and the other faiths have administered to people. The C of E was right to say 18 months ago that this practice should come to an end, and we need to carry that through on the ground.”

Although he had received no complaints about the issue in Liverpool, he said: “I think there is still a work of education to be done in the different dioceses. Bishops need to make sure that local churches understand that LGBTI orientation and identity is not a crime, not a sin and that conversion therapy should be brought to an end.

“If people are made to feel second rate on account of their sexuality or their gender identity, that is wrong. And wherever it happens it needs to be repented of, and I and others need to apologise to anyone who’s been hurt by that. It’s hurtful to be told that the way God made you is wrong and you need prayers to change it. There is a culture change in certain parts of the church which is ongoing, and the only way to fix that is through constant education.”

Jayne Ozanne, who set up the foundation and who underwent conversion therapy resulting in two nervous breakdowns, said: “The scale and severity of the problems reported and the age at which children are said to be exposed to these practices are of the gravest concern. These are serious safeguarding issues which require urgent action.”

Conversion therapy was discredited and caused significant harm, said Martin Pollecoff of the UK Council for Psychotherapists and a member of the foundation’s advisory board. “Our aim is to help people come to terms with their sexuality so that they can embrace and celebrate who they are, rather than living in shame and fear.”