Shocking increases in promiscuity and a culture of high-risk sex among Britain's gay community are threatening to unleash an epidemic of drug-resistant HIV. Johann Hari reports on a disaster in the making

In the spring of 2004, a crystal meth addict slumped into a clinic in New York. His skin was broken with lesions, and he explained to the doctors that he had had unprotected sex - barebacking - with several hundred men in the past year. At first, it seemed like the same kind of case that staggers into Aids clinics across the world every day: gay man gets addicted to crystal meth, belly-flops into a culture of raw sex, and seroconverts in a second. Only this case was different. This man had tested negative just six months before - but he was already showing the symptoms of Aids.

It seemed impossible: the virus takes far longer than six months to progress to its late, lethal stages. And it got worse: the virus ravaging his body was so powerful that protease inhibitors didn't work. The doctors tried cocktail after cocktail, but nothing changed. It seemed like this was a new Patient Zero, and super-Aids - a new, more toxic mutation of the HIV virus, quicker and invulnerable to drug treatment - had arrived.

This was not an idle press scare. Dr David Ho - who had been named as Time magazine's "Man of the Year" in 1996 for his Aids research - issued a warning alongside the New York City Health Commissioner that this was "a wake-up call". Tokes Osubu, executive director of the charity Gay Men of African Descent, said: "This is the news we have all been fearing." But the worst did not happen. It turned out that the men Patient Zero had had sex with were not contracting the same illness - this super-Aids was not super-transmissible - and eventually he did respond to the drugs T-20 and efavirenz. The alarm was switched off. We all went back to sleep.

Some doctors have tried to warn against this narcoleptic response. In February, the HIV physician Dr James Braun warned the 12thConference on Retroviruses that the transmission of treatment-resistant HIV is "a disaster waiting to happen". But the refusal to listen, the determination to keep on barebacking, shouldn't surprise us.

The culture of safe sex that emerged in the wake of the first Aids crisis - when the disease scythed through gay communities - has now melted away. Barebacking has become cool. Check out the darkroom of any gay club and you'll find condomless sex. Click into the chatroom of any pick-up site and there are men - both HIV-positive and negative - advertising for "raw" sex. Nearly 60 per cent of gay British men had unprotected anal sex in the past year - and the rising HIV infections in the US are expected to cross the Atlantic any day now.

But why would gay men play Russian roulette with their genitals? Michael, the webmaster of XtremeSex, a barebacking site, says HIV is now "a minor inconvenience" and "not the catastrophe negatives think it is". Some HIV prevention experts have labelled the new treatments "protease disinhibitors", because they have lulled many gay men into believing that contracting HIV is less like getting cancer and more like getting diabetes, merely a matter of swallowing a few pills a day.

The HIV-positive playwright Larry Kramer is incredulous. "I don't understand why some of you believe that, because we have drugs, it's worth gambling with unprotected sex," he says. "These drugs are not easy to take. There are many side-effects. I have to allow one day out of every week to feel really shitty, to have no sleep, to be constipated, to have diarrhoea, to require blood tests and monitoring at hospital, and to have the shakes. I don't enjoy eating any more. Keeping on weight is a constant problem. I have a dry mouth. I get up six or seven times a night to pee. Is a fuck without a condom worth not being able to taste food?"

It is tempting to blame homophobia for this dysfunctional behaviour, and there is probably a sliver of truth in it. Gay teenagers are far more likely to self-harm - slicing their flesh with razors or knives - than their straight siblings. They internalise the homophobia of the culture around them, and act it out on their own bodies. So is the gay community now collectively self-harming by engaging in wildly risky behaviour? Some of these new seroconversions can be traced to the most homophobic legislation of the past 30 years: Section 28.

The UK Gay Men's Sex Survey recently found that one-third of 20-year-old gay men do not know even the most basic facts about HIV transmission. Some 51 per cent didn't know that HIV is more likely to be passed on if he or his partner has another STD; 31 per cent did not know that water-based lubricant reduces condom failure; and, incredibly, 14 per cent did not know that HIV is more likely to be passed on if a man ejaculates inside his partner. This is the direct product of legislation that made teachers terrified to discuss gay sexual health issues with their students for an entire generation: there are hundreds of HIV-infected teens whose trail of infected blood runs back to Margaret Thatcher.

But at some point gay men have to take responsibility for our actions. We are not robots programmed by homophobia to self-destruct. Look at the choices gay men are increasingly making to use a disastrous drug, crystal meth (also known as crystal, Tina, ice or redneck cocaine, because a hit costs as little as a Big Mac in rural America). In the late 1990s, crystal meth began to transfer onto the gay circuit party scene in the US and today it's used by a quarter of gay men in San Francisco, according to some surveys. Crystal makes it possible to have sex for hours, even days. It simultaneously makes you incredibly horny and melts away your rationality and cautiousness - a recipe for unprotected sex.

Mel, a man who contracted HIV while addicted to crystal, explains: "If somebody wants to shag you without a condom, you just don't care. I did things on crystal I would never do sober." He's not alone: New York's Collen-Lorde Community Health Center has found that two-thirds of their patients who tested HIV positive since June 2003 acknowledged crystal use as a factor in their infection. When crystal meth is twinned with the constant sexual availability of the internet, it becomes a guarantee of rapid HIV transmission. As one journalist puts it: "The internet has turned out to be a higher-risk environment than any bar or bathhouse. Men who meet online are more likely to use crystal, more likely to be infected with HIV, and less likely to use condoms." In this environment, the potential for a mutated super-Aids virus to spread is phenomenally high.

Viruses are constantly mutating: even today, HIV positive men are immune to at least 35 per cent of the available protease inhibitors. A situation where we have a central group of men infecting and reinfecting each other through barebacking, with the most virulent and vicious strains of the virus spreading, almost creates a petri dish for incubating the HIV virus. The viruses we unwittingly create will spread far beyond the gay community. Do we want to see a further levelling of Africa?

Gabriel Rotello, gay author of Sexual Ecology: Aids and the Destiny of Gay Men, explains: "You can't have a core group of people having sex with large numbers of people without amplifying any sexually transmitted disease that enters the system. I don't have any doubt that a resurgent HIV epidemic will hit the gay population in the near future." But, he believes, "people are not going to modify their sexual habits in ways that are difficult or unpleasant until they see their friends dying again. And to me that's just an unbelievably depressing thought."

The gay community is particularly ill-equipped to deal with these looming crises. Peter Staley, a veteran Aids activist and recovering meth addict, explains why: "The whole basis of our community is very libertarian. The gay liberation movement's primary focus has always been fighting against those who are trying to tell us how to live our lives, so we're very reluctant to tell each other how to live our lives. And rightly so. But I hope our community only takes that so far. For example, if we had been completely libertarian during the height of the Aids crisis in the Eighties, there would have been no pressure on some gay men to make other gay men use condoms all the time. That was our greatest hour as a community - when we started helping each other, and expecting that we take care of our own. Now, here we are again, faced with a situation where the health of many gay men is under serious threat. We need to start helping and pressuring each other again."

If we want to avoid a renewed crisis, we have to do something that is temperamentally very difficult for gay people: we have to restigmatise unprotected sex and make crystal meth socially unacceptable. For a community whose whole purpose has been stripping away stigma, this will be wrenching - but the alternative may be another mass culling of the gay population. We should not offer disapproval for puritanical reasons; it's simply a matter of collective survival. As the playwright Jeff Whitty puts it: "I don't care what kind of sex anyone has. But we have a problem. And we need to start dealing with it if we don't all want to die. How many times does that message need to be sent?"

Some campaigning gay groups in the US want to launch an aggressive, full-on campaign against callously risky behaviour. Groups like ACT-UP have proposed sabotaging meeting places for people who engage in deliberately risky behaviour, such as barebacking clubs. Charles Kaiser, historian and author of The Gay Metropolis, argues: "Gay men do not have the right to spread a debilitating and often fatal disease. A person who is HIV-positive has no more right to unprotected intercourse than he has the right to put a bullet through another person's head."

Kramer believes that tolerating the rise of barebacking and crystal makes gay men complicit in a slow-motion massacre. "From the first moment we were told in 1981 that the suspected cause was a virus, gay men have refused to accept our responsibility for refusing to listen. Starting in 1984, when we were told definitely that it was a virus, this behaviour turned murderous. I have recently gone through my diaries of the worst of the plague years. I saw day after day a notation of another friend's death. I listed all the ones I'd slept with. There were a couple of hundred. Was it my sperm that killed them? Have you ever wondered how many men you killed? I know I murdered some of them. Has it never, ever occurred to you that not using a condom is tantamount to murder?"

The Crown Prosecution Service reinforces this message: four HIV-positive people have been convicted in the past year of "biological GBH" for having unprotected sex with people without informing them of their HIV status. "I cannot understand," Kramer says, "how, life having been given back to us again, you treat your life with such contempt."

Yes, it will be tough for gay people to deal with these questions - but if we don't, rising HIV levels and super-Aids may well deal with us. Martin Luther King said: "Our lives begin to end the day we become silent about the things that matter." For the gay community, this is no longer just a metaphor.

A version of this article appears in this month's 'Attitude'