The largest association of psychotherapists in the UK has sent a letter to all of its 30,000 members, telling them that being gay is not a mental disorder and cannot be "cured."
Pointing to a report by the World Health Organisation "Cures For An Illness Which Does Not Exist" the British Association for Counselling and Psychotherapy (BACP) issued a formal change of its policy.
The letter stated that practices such as "conversion or reparative therapies 'have no medical indication and represent a severe threat to the health and human rights of the affected persons'."
The letter comes after Christian psychotherapist Leslie Pilkington was struck off for trying to "covert" an undercover journalist.
She lost her appeal against the decision in May, and while British Medical Association passed a motion condemning conversion therapy after journalist Patrick Strudwick's piece, the BACP was still involved with the case.
The letter issued by the BACP issues a clear warns therapists against seeing the cause of a patient's problem as rooted in their sexuality, insisting:
"There is no scientific, rational or ethical reason to treat people who identify within a range of human sexualities any differently from those who identify solely as heterosexual."
Their change in ethical guidance supports a position long campaigned for by gay, lesbian and bisexual groups.
Ruth Hunt, director of public policy at LGBT charity Stonewall said: "We're delighted that voodoo 'gay cure therapy' can now be treated with precisely the same seriousness as bloodletting and trepanning [an ancient 'cure' for mental health issues in which a hole is drilled in the skull. It is an ineffective and often resulted in the patient's death.]"
However Phil Hogson, a spokesperson for the BACP told the Telegraph the association's hands were tied as they could not alter their official guidelines until the case had been closed.
In May, an advert that promoted gay conversion therapy due to run on London buses was banned following a public outcry.
The adverts featured the slogan "Not gay! Ex-gay, post-gay and proud. Get over it" in a mirror image of Stonewall's flagship "Some people are gay, get over it" campaign.
They said that the Stonewall campaign, which was launched at the start of April, "implies the false idea that there is indisputable scientific evidence that people are 'born gay', and that they have no choice but to affirm their homosexual feelings".
The groups also warn against the "misleading and dangerous" effects of the "promotion of homosexual practices to children and young people" and that people should be "supported in developing their heterosexual potential".
The adverts were pulled from buses after a public outroar. TFL said at the time:
"We do not believe that these specific ads are consistent with TfL’s commitment to a tolerant and inclusive London."