When Derren Brown revealed yesterday that years ago he "flirted" with an evangelical group that attempted to "cure" his homosexuality, one thought reverberated through me: he's dodged a bullet.

For several months I went undercover and infiltrated these dubious organisations. I put myself through so-called "conversion therapy" with a British psychiatrist and a psychotherapist. Through counselling they tried to find the childhood "wounds" that made me gay and "heal" them. They suggested I take up rugby and have non-sexual contact such as massages with men. At a conference I saw a young gay man being "treated" in front of a live audience.

When my investigation was published, scores of victims contacted me. I saw the self-harm scars. I heard again and again about the suicide attempts caused by these failed attempts to become heterosexual and the years of follow-up therapy they needed to recover. Some never really did. One man told me that as recently as the mid-80s, when he was 16, an NHS psychiatrist offered him electro-convulsive therapy for his homosexuality.

A study by the psychologists Ariel Shidlo and Michael Schroeder found that conversion therapy caused psychological damage in a majority of cases. Every major mental health body in Britain condemns it. Yet the coalition government is failing to protect patients against this psychological snake oil. Rather than pushing ahead with the previous government's plans to regulate counsellors and psychotherapists, they propose a voluntary register. A central, transparent body is needed to discipline those involved in conversion therapy. Vulnerable gay people who stumble into the "care" of fundamentalist therapists need protecting – before more young lives are ruined.