There are many reasons to be upset by the violent death of Grace Millane, the backpacker from Essex who was murdered a year ago in a New Zealand hotel room by a man she met on the dating app Tinder. Speaking after her killer (whose name has yet to be released) was convicted, the victim’s father described the murder of his “beautiful, loving, talented” daughter as barbaric. Since she was strangled on the eve of her 22nd birthday, the 27-year-old murderer has continued to inflict pain.

The defence offered at his trial, that the death was the accidental result of a sex act that she had requested, meant that her parents sat through a trial in which intimate details were picked over and broadcast across the world. New Zealand has the reputation of a safe, welcoming country. It is horrifying to know that this young woman’s trip of a lifetime ended with her bruised body being stuffed into a suitcase and buried in the bush.

To learn that these appalling events are part of a pattern adds to the horror. In the last five years, 20 UK women have been killed by men who used “rough sex”, often involving strangulation, as a defence. In around half of these cases, the defendants have either not been jailed or had sentences or charges reduced (from murder to manslaughter or, in Scotland, culpable homicide).

Another factor that links cases of women killed or injured during sex is the role played by pornography. Ms Millane’s murderer viewed clips of child sexual abuse after he killed her, and took photographs of her body. In four out of the last 10 killings of this kind, perpetrators watched pornography either immediately before or after.

The internet has enormously enlarged the audience for porn, and changed the nature of the content – with user-generated and more extreme varieties more prevalent. Now, the sharp increase in the use of the “rough sex” defence, combined with the rising popularity of once-niche BDSM practices such as choking, appear to show that sexual behaviour is changing. The law needs to catch up. Consenting adults who engage in alternative sexual practices should not be criminalised because other people find these distasteful. But action is needed to reduce the risk of people being seriously harmed (seven UK men, as well as 59 women, have been killed by men who blamed “rough sex”), and to prevent victim-blaming of the kind seen in the Millane trial.

The Labour MP Harriet Harman is leading efforts to amend the domestic abuse bill in such a way as to eliminate the defence of consent in cases of actual bodily harm, serious injury or death (bringing into statute a prohibition that already exists in case law). The next parliament should support these changes. New Zealand, where Millane was murdered, should consider similar steps. An age verification system intended to restrict access to pornography was cancelled last month and the next government must not duck the challenge of regulating the internet because it is difficult. As a first step, ministers should invest in research to strengthen understanding of pornography’s influence in society. The domestic abuse bill is just one element in what must become a much bigger effort to reduce intimate partner violence, the majority of which is inflicted on women and girls.