Human rights and Green activist Peter Tatchell is organising protests against hardline Christian churches in Britain which perform "exorcisms" on lesbian and gay people in a bid to purge them of their homosexuality.
"The exorcism rituals involve the casting out of alleged demons and witches that supposedly possess a gay person's soul and turn them away from heterosexuality," said LGBT campaigner Peter Tatchell from the OutRage! group.
He is urging people to write letters containing "calm, compassionate, rational arguments" to one pastor involved - but also says that he should be reported to the police and his MP.
"There are claims that gay teenagers and young adults are being subjected to exorcisms at the insistence of their parents and pastors, in an attempt to rid them of same-sex attraction", says Mr Tatchell.
"The exorcisms can include traumatic emotional scenes where the victims are surrounded by a group of church elders who scream at them to drive out the evil spirits and who sometimes shake their bodies.
"When this is done to youngsters under 18, it is a form of child abuse and the police should intervene to stop it
"Some gay adults have been pressured into exorcisms by their family members or faith communities. Other victims are people with learning difficulties or mental health problems. They have been preyed upon when they are in a vulnerable state and are not capable of giving fully informed consent.
"There needs to be a thorough police investigation of all the churches that are doing these exorcisms," added the human rights campaigner.
One London church admits it does exorcisms on four or five gay people every year. This church, United Pentecostal Ministry in Harrow north London, was exposed by The Metro newspaper late last month.
The church's pastor, the Rev John Ogbe-Ogbeide, said he did the ritual to cast out the demons and evil spirits that he believes are responsible for homosexuality. Sometimes people were calm during the process but sometimes their body convulsed, he conceded.
Exorcisms can be performed on gay children or on those who are suspected to be gay. There is no minimum age for the exorcism ceremony because a demon could possess a person at any age in life and could incline them to "wrong" sexual thoughts and behaviour, said Rev Ogbe-Ogbeide.
Mr Tatchell commented: "United Pentecostal Ministry says it performs four or five exorcisms on gay people each year. It is just one of hundreds of fundamentalist churches in Britain. Gay exorcisms are likely to be performed in many of them. It is possible that dozens or even hundreds of LGBT people could be subjected to exorcism abuse in the UK. Because it takes place behind closed church doors and is kept secret, it is impossible to give an accurate assessment of the numbers involved."