Joan Smith: Sarah Jane deliberately infected her lovers with HIV out of revenge. Says who, exactly?

Was it accidental that the photos used recalled Myra Hindley?

When Sarah Jane Porter found she was HIV-positive, she was so angry that she embarked on a mission to pass on the virus to as many men as possible. Porter, who is white, became HIV-positive after a relationship with a black man and directed her rage at young black men she met in clubs up and down the country. When one of her victims went to the police, she refused point blank to help them, forcing detectives to appeal for more of her "countless" sexual partners to come forward. On Monday, Ms Porter pleaded guilty to a charge of recklessly inflicting grievous bodily harm on another man and was sent to jail for 32 months.

There's just one problem with this lurid tale of a heartless Aids avenger: it isn't supported by the evidence. And while a sick single mother spends her first weekend in jail, separated from her six-year-old daughter, the case raises important questions about sexual mores and individual responsibility in our Aids-aware culture. In a week when research sponsored by the Home Office confirmed that barristers and judges are getting round rules designed to protect rape victims from intrusive questioning about their sexual history, it also offers compelling confirmation of the double standards and misogyny of the criminal justice system.

The new report shows how the rules, introduced in 2000, have been "evaded, circumvented and resisted" in rape trials; the researchers argue that defence and prosecution lawyers continue to share stereotypical assumptions about "appropriate" female behaviour, leaving victims to face aggressive questioning about their sex lives when they are in the witness box. As a consequence, legislation designed to increase the conviction rate in rape cases reported to the police - currently at an all-time low of just over 5 per cent - has had little or no effect. Unless women are making massive numbers of false allegations, a proposition not supported by evidence, 19 out of 20 rapists are getting away with it.

Contrast this with the way the criminal justice system has dealt with Ms Porter, whose conviction alarmed hundreds of people who have just had or were about to have HIV tests. Many of them phoned the Aids charity, the Terrence Higgins Trust, desperate for advice following her trial. It is not a criminal offence for people who suspect they are HIV-positive to have unprotected sex; and some people are bound to wonder if it would be safer, in legal terms, not to know their status. In that sense, this one case could single-handedly derail the Government's safety-first policy, leading fewer people to risk having a test.

At the same time, after an initial spate of extremely hostile publicity, people have begun to ask whether jailing Ms Porter, a 43-year-old secretary at the West End training college of the Vidal Sassoon hairdressing chain, actually achieves anything. There is simply no evidence for the most lurid accusations: that she deliberately infected men with HIV or set herself up as some kind of Aids avenger. The facts suggest that while she was in denial about her HIV status - and no one would argue that she did not have a responsibility to inform her partners - she was involved with a series of men whose own sense of moral responsibility is open to criticism.

Far from contracting the virus during a one-night stand, she was infected by a long-term lover, the father of her son, who deserted her after the child's birth. The only man she is known to have infected is another long-term partner, a 31-year-old disc jockey and promoter, who stayed with her for 18 months after his diagnosis.

The man who went to the police, identified only as "Mr B", had a three-month relationship with Ms Porter after they met at a nightclub but did not contract the virus. "I went to the police because there was no way she could get away with this," he raged in the Daily Mail. They "sometimes" used condoms, but Ms Porter "didn't seem bothered if they broke". Neither, it seems, did "Mr B".

It is worth pointing out here that the virus hasn't just arrived in this country; only someone who had spent the past two decades on Mars could be unaware of the risks of unprotected sex, and men are as free to insist on using condoms as women. Yet Ms Porter seems to have moved in a world where it is up to women to shoulder all the responsibility, as the ex-partner to whom she passed the virus made clear after the trial. "As my girlfriend, she was meant to care for me and support me and I trusted her to do this," he declared.

In fact, the man initially believed that it he who had infected Ms Porter, for reasons that became clear only in medical reports prepared in the run-up to the trial. That was when Ms Porter, who believed she had been in a monogamous relationship, was astounded to discover that he had been having sex with three other women. This is not to excuse her conduct, but it hardly justifies the way she was presented in the media last week: was it really an accident that the most widely used photograph of Ms Porter, with dark roots showing in her blond hair, recalled the mugshot of the Moors murderer Myra Hindley? She was told by police at one point during her interrogation that she was "no better than a murderer", and the Mail was just as hostile, giving one of her former lovers space to denounce her as "pure evil".

Rape victims frequently say, after appearing as witnesses, that they felt as if they, not the defendant, were on trial. After three decades of feminism, during which women have rejected the double standard and insisted on the same right to sexual autonomy as men, this is the forum in which a huge disconnect becomes apparent. Punitive attitudes to sexually active women are still widespread, along with an irrational conviction that women are deceivers whose word - about paternity, consent and now disease - cannot be trusted.

When a woman is actually in the dock, as Ms Porter was last week, it is regrettable but not surprising that wild allegations will be flung at her. What is astonishing is that so many commentators repeated a farrago of misogynist fantasy as if it were the truth.