A group which offers to "cure gays" is to campaign in parliament against a move to outlaw the practice.
Christian organisation Core Issues Trust is to host a conference at Westminster in support of its therapy, which it claims helps people to "change unwanted same-sex feelings".
Critics said it risked causing mental problems for people who undertook it. But supporters said it should be a person's right to undergo treatment if they wanted it.
A Bill in parliament seeks to outlaw so-called gay-to-straight conversion therapy under wider regulation of the psychotherapeutic industry which is currently not regulated at all.
The Bill has been put forward by Labour MP Geraint Davies who will address the Core Issues Trust conference.
He told IBTimes UK: "People who may be feeling confused about their feelings may find themselves in the hands of someone with an agenda of imposing their worldview. I do not think a national and paid-for service should be in the business of imposing an alien sexual orientation. It's in conflict with the patient's rights."
The treatment for altering sexual orientation, known as reparative therapy, has been condemned by the British Psychological Society (BPS). Dr Lyndsey Moon told IBTimes UK: "The evidence says that conversion therapies are not acceptable and they are likely to lead to more problems, such as depression, anxiety and confusion.
"That's not acceptable. People do not need to be cured and are not any way pathological."
Moon asked why the BPS had not been invited to the event at parliament. She said: "Surely the issue should get fair scrutiny. If you are going to hold a meeting at parliament then why not hear all sides?"
A Core Issues spokesman defended its programme: "It's not conversion therapy. It's about assisting people to change from unwanted sexual attraction if they want to have this therapy."
Condemnation of the group's treatment has been near universal, following an advert containing the slogan "post-gay" it ran on buses in 2013.
Business psychologist Lee Robinson, who is gay, told IBTimes UK: "What is it about our society that leaves some people feeling that having a sexual orientation that's not heterosexual is unwanted or abnormal?
"This quackery should be regulated against to protect potentially vulnerable individuals from misguided supposed professionals."
Last year, one million people in Britain accessed treatment from the unregulated mental health therapy industry. If passed into law, the Counsellors and Psychotherapists Bill would put the industry under the Health and Care Professions Council.