dElia Balmer is lying on her bed in a small, sparsely furnished apartment. She is now in her seventies, but the camera shows her reliving a painful memory from almost 40 years ago. “He tied my ankles,” she says, leaning back over the star-shaped covers. “He grabbed my hands; tie that one first, at the top” – she points to her left arm – “And then the other one at the top. At first, I struggled, but I learned it’s better not to struggle because he fixed it so the rope got tighter and tighter.”

The bed she’s lying on is the exact same one John Patrick Sweeney made for her, the same one they shared while living together after they started dating years ago. It’s the same bed where, in 1994, Sweeney tied her up before holding her hostage and raping her repeatedly for a week.

In that bed, she found out who her lover really was: a serial killer who preyed on women. “He threatened to cut out my tongue if I screamed,” says Delia. She lay silent and blank as he made a chilling confession – that he killed his ex-girlfriend, Melissa Halstead, before cutting her up and dumping her body in an Amsterdam canal.

Over the past week, ITV viewers have watched the retelling of Delia’s harrowing ordeal in a stunning four-part drama. Until I kill you in which Anna Maxwell Martin plays Delia to extraordinary effect.

Her critically acclaimed portrayal of Delia reveals an independent and socially awkward woman whose purpose in life seems to be the pursuit of freedom, but who then becomes a prisoner of extreme male violence.

Following Maxwell Martin’s strong performance coupled with the stunning incompetence of the police involved in her case, the audience was left in shock, wondering what happened to the real Delia.

A subsequent documentary on ITV – Until I Kill You: The Real Story – answer this question in some way. In the 45-minute programme, Delia, who still lives in London, speaks candidly to the camera, explaining her side of what really happened – and what her life has been like since.

“She’s an amazing person,” says series producer Iwan Roberts, who spent a year making the film. They would go to the pub in Camden for a pint, he says, where she would tell ‘fantastic anecdotes about traveling the world’, he explains, adding: ‘She’s a delight to talk to.

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Maxwell Martin plays Delia as a difficult and often irascible loner – and also shows us glimpses of her vulnerability. Her character brings to life the complexities that can surround victimization – especially when it comes to male violence.

“I think he’s a very different person than a lot of people,” Roberts continues. In a scene that will shock some viewers, Delia shows the filmmakers the massage table Sweeney built, showing his signature in black marker underneath. “One of the reasons he keeps all the furniture Sweeney made for him is because he doesn’t see things like we do. She wants to spend her money on travel, so she doesn’t mind.”

“She says she wishes she was dead after Sweeney attacked her,” Roberts says. Today, Delia says that despite not being killed, she died that night, but Roberts adds that “I would imagine she might not say it, but she still has a huge zest for life.”

Delia’s story began after she settled in London to work as a nurse, although her childhood was spent mostly in Canada. He met Sweeney by chance in a bar. He was a carpenter by trade; tall, broad, dark, with long hair. Like Delia, she valued freedom and exploration. The pair formed a relationship, which for a while, was happy.

The abuse began quietly – comments about a short skirt she wore, whether men looked at her. He knew he had to go, Delia explains in the film. As in many cases of domestic violence and as it highlights The IndependentHis ongoing campaign with Refuge, this proved to be the most dangerous point.

Delia asked Sweeney to leave, but he returned, threatening her with a gun and a knife, and began a week-long jail ordeal. Amazingly, she managed to get him to let her go, spending the next few months terrified that he would return – or retaliate if she told the police.

He found gruesome drawings that Sweeney had kept in a portfolio: women with missing heads and hands, miniature carpenters hacking apart a woman’s body. When a counseling center she eventually went to for help called the police, she showed investigators evidence that she was a criminal. They dismissed her claims – and Sweeney was nowhere to be found.

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Sweeney inevitably returned. After attacking Delia again at her flat, a friend of hers called the police after sensing something was wrong after Delia failed to show up at the pub. He was eventually arrested but, shockingly, was released on bail at Christmas.

On December 22, Sweeney attacked Delia outside her home as she was returning from work. He was armed with an ax and a knife. “He takes out the axe, hits me on the side of the head,” Delia explains matter-of-factly to the camera, sitting on the very steps she was attacked on so many years ago.

She explains how she raised her arm to protect herself, which was fractured by another blow. Finally, he drops the ax and raises the knife, stabbing her in the thigh before plunging it through the chest.

Sweeney was interrupted by a concerned neighbor, a simple act that saved Delia’s life, but decades later she insists, in her opinion, he killed her that day. She spent months recovering in hospital and throughout the documentary, she refers to “this body” saying that even today she can’t recognize herself in the mirror and still struggles with depression and anxiety.

It took the police almost ten years to bring Sweeney, who was on the run, to justice – and Delia was repeatedly let down by the law in almost every case. The scenes of the male cops not taking her seriously or screaming in court when they give their first testimony at her trial are hard to watch. Deeply traumatizing, it’s a visceral indictment of how women and their bodies are routinely and casually rejected by violent men and often by the systems that are meant to protect them. Years later, that anger remains.

“He doesn’t let people see his vulnerability,” says Roberts. He is a very proud person and doesn’t want to show that emotion or all that he carries. Sometimes she can be prickly or come across as grumpy.” But, he says, this is the result of a life besieged and defined by an ordeal she claims she “will not accept” what happened to her.

Sweeney was eventually convicted of Delia’s attempted murder and, much later, of the murders of two other women – Melissa Halstead and Paula Fields, becoming known as the ‘Scalp Hunt’.

In the documentary, Delia’s brother Stewart describes a strange encounter with Sweeney that ruled out that name. “I asked him, have you ever killed anyone? I don’t know why I asked him, he just had these vibes about him,” says Stewart. “He didn’t answer yes or no. He said, “The white men taught the Indians how to scalp.” Really weird.”

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After the law failed Delia again by giving Sweeney the option of parole after serving just nine years, his subsequent convictions saw his sentence increased to a full life term. He was convicted in 2011 while serving a life sentence for Delia’s attempted murder in Gartree Prison, Leicestershire, and will never be released.

Today Delia continues her life as best she can. A dancer, “ballet is very important to her,” explains Roberts, “and she still enjoys traveling to India and Africa. She also visits her brother Stewart in America once a year.” She now works as a masseuse therapist after gaining a degree from the University of Westminster in the early 2000s. In 2017 she wrote a book – Living with a serial killer — about her experiences, which formed the basis of the drama, something she wanted to do, says Roberts.

Telling the story was crucial. She needed to be heard. And now, her incredible stoicism and strength in the face of horror is on display for all to see.

Still, she bears the scars of Sweeney’s brutal attack. But Delia and the makers of the ITV drama hope the courage to tell her life story will give us all a deeper understanding of the survivors’ suffering – and highlight a system that fails women like Delia time and time again.

Until I Kill You: The Real Story is on ITV1 at 9pm tonight (November 7). Until I Kill You is available to watch on ITVX

Please donate now to the Brick by Brick campaign, launched by The Independent and charity Refuge, to help raise £300,000 to build a safe space for women where they can escape domestic abuse, rebuild their lives and and make a new future. Text BRICK to 70560 to donate £15.

The National Domestic Abuse Helpline offers support for women on 0808 2000 247 or you can visit Refuge website. There is a dedicated men’s advice line on 0808 8010 327.