Feminist Harriet Wistrich had been a solicitor for 20 years, many of them with the noted human rights firm Birnberg Peirce (the Guildford Four, the Birmingham Six) when, aged 55, in 2015, she decided to have a rethink. She and her partner, campaigner Julie Bindel, embarked on a three-month sabbatical tour visiting Canada, South Korea, Cambodia and Vietnam, during which Wistrich developed the idea of a legal charity that would “tackle state accountability for all types of violence against women by undertaking the litigation specifically aimed at system reform through legal action”. In short, she would set out to remodel parts of the law so that it offered justice not just to men, as it has done for generations, but also to women who, all too often, have been abused, traumatised and discriminated against long before an appearance in court.

So in 2016, Wistrich founded the Centre for Women’s Justice (CWJ) to tackle a system that is not fit for purpose. Staffed by a tiny team, it’s powered by Wistrich’s tenacity, compassion, focus and inventiveness, evidenced in the 10 cases stretching back to the 1990s she describes in the book. The cases powerfully lay bare the appalling inadequacies of the police, the duplicity, arrogance and bone-headedness of the Met particularly and the blindness of the patriarchy to the female experience.

The book begins in the summer of 1991 when Wistrich and Bindel are campaigning for Sara Thornton, a woman serving a life sentence for killing her violent, alcoholic husband. At the time, the partial defence of provocation had its origins in the 16th century, available to men who killed in “justifiable anger” in the heat of the moment because of an insult to their honour.

“It was a law designed for men who kill in anger, not for women who kill out of fear,” writes Wistrich. The Free Sara Thornton campaign eventually became Justice for Women, co-founded by Wistrich and Bindel, championing women such as Emma Humphreys, who killed her brutal pimp at the age of 17. The seeds of CWJ were sown.

At about the same time, Southall Black Sisters, a domestic violence service and feminist activist group that supported black and Asian women, was campaigning for the release of Kiranjit Ahluwalia, who had endured years of rape, beatings and house arrest at the hands of her husband. She had set fire to his bedclothes in an attempt to escape and he had died.

Thornton, Humphreys and Ahluwalia were all eventually released. The publicity about their cases ensured that the public became aware that “justice” could be sexist and discriminatory. Could that injustice be challenged?

Wistrich’s answer is yes. Litigation can take years; she thrives on perseverance. In the book, she describes how in 2011, she began the fight to free Sally Challen, who was convicted of murdering her husband, Richard, with a hammer after three decades of horrendous abuse. She was sentenced to a minimum of 22 years in jail. Challen was eventually freed in 2019 after pleading guilty to manslaughter. Wistrich and her allies, including barrister Clare Wade KC, achieved a landmark ruling: it was the first time a court had considered a “coercive control” defence, accepting it as a form of domestic abuse. Judges are now required to treat years of abuse including coercive control as a mitigating factor when a woman is provoked to finally kill.

The other cases Wistrich covers in the book include the fight for justice and compensation for eight women who were tricked into relationships, and some bearing children, with undercover police officers from the now disbanded Special Demonstration Squad, a unit within Special Branch. Incredibly, the Met initially said this behaviour was no worse than a husband lying to his wife about an affair. A public inquiry that began in the summer of 2015 into undercover policing spanning more than half a century was intended to take three years. Wistrich writes that it is not expected to be completed until 2026. What is already known is that more than 50 women, so far, have been in long-term relationships with men they were unaware were undercover officers. Wistrich warns that the adoption of the so-called “Spycops” act in 2021 means that further victims of undercover cops could be denied the right to bring a claim for compensation. She writes: “Most of the women had devoted years to nurturing a relationship that was never going anywhere and some had spent many more driving themselves mad searching for a man who did not exist.”

Then there was the appallingly bungled police investigation into taxi driver John Worboys, who raped and sexually assaulted more than 100 women, brutally offending for years. He was eventually arrested and found guilty of 12 of the cases. While he was still in prison, the Parole Board, without an obvious rationale, decided that it was safe for him to be released. The CWJ and women he had violated successfully prevented his release by reminding the Parole Board that Worboys had committed crimes against many more women than the 12 for which he had been prosecuted. Reforms have since been made to how the Board operates.

In 2018, the government opened up a new avenue for accountability in the form of police “super-complaints”. It allows designated organisations to raise questions on behalf of the public about harmful patterns or trends in policing.

The CWJ became one of 16 designated bodies selected by the Home Office. Designated bodies can submit a super-complaint that is first assessed by HM Chief Inspectorate of Constabulary, the Independent Office for Police Conduct and the College of Policing; a high bar. If accepted, the three agencies then investigate and make recommendations for change.

The first highly significant CWJ super-complaint concerned the failure of police forces to make proper use of the powers they have to protect women facing domestic abuse. The second, equally important, addressed police-perpetrated domestic abuse. Both were successful. A year later Sarah Everard was raped and murdered by policeman Wayne Couzens, followed by a series of cases revealing all too clearly a deeply misogynistic culture in policing. Recommendations from both super-complaints are now under way.

Wistrich’s skill lies in her innovative use of legislation, especially the Human Rights Act (1998), which includes the right to privacy, the right to life and the right not to be discriminated against. The book reveals how she combines this with a deft use of the media and, on occasion, crowdfunding, so that in her legal high-wire act, clients are protected from going broke if costs are awarded against them. “Not every battle ends in victory,” Wistrich writes, “But we always make a mark.”

• Sister in Law: Fighting for Justice in a System Designed by Men by Harriet Wistrich is published by Torva (£22). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply