"How many of you are in need of some hope here tonight?” A murmur passes through the dark auditorium, pleasing the man with the microphone. Heads nod. “How many of you are at the end of your rope?” he continues. “How many are ready for an encounter with the Lord?” The man on stage, dressed in chinos and a crisp white shirt, is Alan Chambers. The clean-cut, married father of two is the leader of Exodus International, an organisation that believes it can help people to “find freedom from homosexuality through the love of Jesus Christ”.

Exodus is one of the ministries of the so-called “ex-gay” movement, a controversial fundamentalist Christian campaign that encourages gay people to renounce their sexuality. This, its annual conference, promises “an amazing week of breakthroughs, transformations and healings”. A Christian rock band begins to play and the 800 men and women who moments earlier seemed to have only awkwardness in common begin singing and clapping in unison. Eyes closed, they raise their hands above their heads, uplifted by the hope of being reborn.

Chambers later returns to the stage and stands before them, triumphantly heterosexual. He tells the crowd that he won't judge homosexuals, even if their own churches have, because he used to be one himself. In the hushed auditorium, he describes his first experience of a gay bar. “It was almost as if I'd grown up handicapped and everyone else was handicapped, too. But it was a counterfeit. I was fooled.”

“Am I in denial?” he asks. “Absolutely. I live a life of denial and I love it. I didn't choose my same-sex feelings but I do choose how I'm going to steward them. Freedom is possible.” At Exodus people are not gay; they “struggle with same-sex attraction” (SSA).

“The opposite of homosexuality is not heterosexuality,” says Chambers, sagely. “It's holiness.” Speech over, he asks people to come forward to be prayed for. A boy of no more than 16 steps up, hanging his head. When he returns from the stage to the sound of applause, his stony-faced father nods in approval. His mother weeps.

Welcome to ex-gay boot camp.

The belief that homosexuality can be overcome has been fuelling controversy in the US for decades. Although research supporting SSA therapy has been discredited, “ex-gay” ministries are expanding worldwide, even in the UK, where a discreet network practises SSA therapy under the umbrella of “Christian counselling”.

Consider the crisis within the Anglican community over homosexuality, and Exodus begins to offer a strangely seductive solution to reconciling faith and sex. Yet it has been claimed by critics, many of whom have undergone treatment themselves, that some same-sex attraction therapy can exacerbate anxiety and depression, in extreme cases leading to suicidal feelings.

Ridgecrest Retreat is a white, antiseptic blot in the blue-green Smoky Mountains in North Carolina. Masquerading as one of the hundreds of “homosexual strugglers” who visit the Exodus campus, I arrived here after registering online for six days of evangelism psychotherapy.

New arrivals are greeted by a row of friendly staff. Eric, a perfectly coiffured team member from Florida, puts his hand on my shoulder and promises me a “very impactful” experience. Name tags (to be worn at all times) are distributed, as is a schedule of workshops and worship sessions, and room keys. It strikes me as slightly cruel that an event for people battling with their homosexuality should offer shared rooms with strangers of the same sex.

My roommate is Michelle, a 28-year-old who has recently broken up with her girlfriend. A nurse from Ohio who likes Metallica and Christian rock, she has a natural shyness offset by a hearty laugh.

“I used to be out and proud so I can't believe I'm here and not protesting,” she says, “but I wanted to see what it was all about.” This is her first conference and she is accompanied by a support group of impossibly cheerful women, all of whom are ardent believers in the Exodus philosophy.