History was made this week. For the first time, a therapist was found guilty of malpractice after trying to "treat" a client for their homosexuality – to turn them straight.

For decades, mental health professionals used torturous techniques, such as chemical castration, to try to "cure" homosexuality. As recently as the 1980s, electro-convulsive therapy (ECT) was inflicted on gay patients. More recently, a talking therapy called conversion (or reparative) therapy has been used. Now, finally, one psychotherapist – Lesley Pilkington – has been brought to account.

I made the complaint against her. In 2009, I went undercover for this newspaper to investigate the dark arts of conversion therapy, the premise of which is that homosexuality is the result of childhood "wounding" that must be "healed".

And so, Ms Pilkington, a 60-year-old Christian, tried to find what wounded me in a bid to convert me to heterosexuality. This involved the sinister (suggesting I was sexually abused as a child, and praying to God to bring repressed memories to the surface) the dangerous (opining that God heals HIV, and homosexuality is a mental illness) and the ludicrous (advising me to take up rugby).

Britain's largest professional body for therapists, the British Association for Counselling and Psychotherapy, found her guilty of "professional malpractice" last year but she appealed. On Tuesday, however, she lost her appeal when the BACP upheld its verdict. The appeal panel described Ms Pilkington's practices as "unprofessional", "dogmatic" and "negligent" and suspended her. Only if she can satisfactorily demonstrate that she has learned from her mistakes will she be reinstated.

It might be tempting to laugh at techniques used in conversion therapy – find me a gay man who feels less gay after being in a rugby scrum and I'll happily renounce my homosexuality. But, tragically, countless people in Britain and around the world know what damage this kind of "treatment" does.

A 2002 study by the clinical psychologists Shidlo and Schroeder found that 55 per cent of people who go through this are left with worsened mental health – depression, self-harm, lower self-esteem and suicide ideation. I've met some of these people and seen the scars. I fought this case for them.

But even the investigation itself had wide reverberations. Victims of conversion therapy, along with therapists who used to practice it before realising their mistake, contacted me to describe the years of misery they suffered. It spawned protests outside a conversion therapy conference. And the British Medical Association passed a motion condemning attempts to "cure" sexual orientation and urging the NHS to investigate where it might have inadvertently paid for such "treatment". (Ms Pilkington, who was attached to an NHS GP surgery, claimed she had had clients referred to her for conversion therapy by the doctor. The surgery denied this.)I was delighted with the BMA motion and I'm delighted by the BACP's decision. But much as this verdict is a victory for gay people, and for the credibility of psychotherapy, it exposes a gaping flaw in Britain's response to mental illness. There is no statutory regulation of counsellors or psychotherapists. Anyone can call themselves a therapist, without any training or experience. You don't need to be a member of a professional body such as the BACP to charge vulnerable people for your time.

And, thus, Lesley Pilkington can carry on practising for as long as she likes. But the Coalition has shelved Labour's plans to bring in regulation. Instead, it plans to introduce a voluntary register, which will provide no protection or standardised care for the public. This is a scandal. It means that private, independent bodies such as the BACP simply regulate themselves.

Here are two examples from my case to illustrate why this does the public a gross disservice. At the appeal hearing, against its own protocol, the panel let Ms Pilkington cross-examine me directly, for 90 minutes. Imagine what effect that would have on someone whose complaint was of sexual assault.

Secondly, if you complain about a doctor to the General Medical Council, it provides you with a lawyer. The BACP does not, and nor do any similar bodies. So I had to find my own – the eminent barrister Sarah Bourke – to work for me for free. Without her I would not have been able to fight this case. But how many members of the public can access a pro bono lawyer?

Moreover, the BACP’s ruling was a judgment against Ms Pilkington’s methods and practices in this case; not against the use of conversion therapy as such. Until the Government steps in, people at risk can be preyed upon (or, in my case, prayed upon) with no means to prevent the perpetrators endangering others.