The killer of British backpacker Grace Millane has been sentenced to life in prison in New Zealand. Millane’s mother, Gillian, told her daughter’s killer: “You have taken my daughter’s future and robbed us of so many memories that we were going to create.”

The horrific murder of Millane, who met her killer (who cannot be named for legal reasons) on a Tinder date, has focused attention on the increasing use of the “sex game gone wrong” defence by men who kill women. It’s a defence that can only be described as victim-blaming taken to its most grotesque extreme. Here we have increasing numbers of men blaming women for the fatal violence committed against them, suggesting women can somehow consent to their own deaths (which is legally impossible) while claiming they themselves cannot be held responsible. It’s time the use of this defence stopped – for good.

In a twisted reversal, the defence also positions men as hapless victims of women’s sexual demands. After all, how can it be his fault if he was just doing what she wanted? It argues men don’t know that, for example, strangling, beating and cutting a woman’s neck isn’t dangerous, and so they cannot be blamed.

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But that’s nonsense. Millane’s killer strangled her for 10 minutes. As the sentencing judge explained, that’s not “rough sex”. It’s violence.

The campaigning group We Can’t Consent to This, which tirelessly records the use of this defence, believes “sex game gone wrong” was first used in 1972, when Carole Califono died after her partner Peter Drinkwater injected her with anaesthetics. He argued he was trying to “satisfy her perverted sexual desires”, and was sentenced to 12 years for manslaughter.

For 40 years the use of the defence was relatively rare. But since 2010, it has rocketed by 90%, with 28 cases of men claiming a woman died as a result of a “sex game gone wrong”. The oldest victim in the past 10 years was 66-year-old Lesley Potter – although this was just one of many excuses used by her killer. The youngest was 16-year-old Hannah Pearson, whose death I can’t think about without starting to cry. James Morton killed Hannah hours after they met, saying she “didn’t object” when he started to strangle her. He was convicted of manslaughter.

Morton and Drinkwater aren’t the only men who have used the defence. Six cases since 2010 led to a manslaughter conviction, including that of Natalie Connolly in 2018. She sustained 40 injuries and was left for dead at the foot of a staircase. Her killer, John Broadhurst, argued it was rough sex, and was sentenced to 44 months.

The defence also re-victimises the women it is used against, and victimises their families.

During the trial of Millane’s killer, the use of the defence led to her sexual history being raked over the coals. Tabloid headlines in the UK and around the world joined in with the killer’s claims by focusing on her dating past. The New York Post, in a particularly egregious headline, repeated without question her killer’s claims of what she asked for in sexual terms in the hours before her death. Other news outlets chose to focus on her membership of a fetish website, and her alleged requests for BDSM practices.

Of course, Millane can’t defend herself against his claims and the headlines his words spawned. Dead women don’t get a voice. Meanwhile, the people who knew and loved her had to listen to a panoply of voices shift blame from the man who strangled her on to a 22-year-old woman for daring to have a sexual past.

Such victim-blaming leads to another terrifying consequence of the sex game gone wrong defence. If past consent to certain sexual acts can be used against a woman in court then any woman who has ever expressed her sexuality in a certain way can be blamed for the violence committed against her. That is deeply troubling.

Since the Millane verdict there have been renewed calls for the law, in the UK at least, to be changed so men can no longer claim “sex game gone wrong” in court. The Labour MP Harriet Harman has led the charge, calling it the new version of the “nagging and shagging” or “provocation” defence that was banned in 2010. Boris Johnson also backs a ban, according to Grazia magazine.

Such a ban cannot come soon enough. Without it, men will continue to blame their victims for the fatal violence committed against them. Violent men will continue to claim that bruises and cuts are proof of their victim’s consent, as opposed to marks of aggression. And women and families will continue to be re-victimised by lurid claims like those directed at Grace. Claims she could not defend herself against because he took away her voice. He took away her life.

• Sian Norris is a freelance journalist writing about feminist and LGBTIQ issues