Anna Maxwell-Martin's surprising revelation about meeting the real Delia Balmer for Until I Kill You role

Until I Kill You has drawn in record audiences after it started airing on and it tells the harrowing true story of Delia Balmer, who survived a near-fatal relationship with murderer John Sweeney.

Anna Maxwell Martin took on the role of Delia, with Shaun Evans playing the serial killer. The drama narrates the ordeal Delia suffered at the hands of John Sweeney, and her traumatic journey through the police and criminal justice system.

The Motherland actress admitted she did not speak to the real Delia before she started filming, saying: "I’ve played quite a few real people and I have never met them before. I don’t choose to do that, that’s how I work.

"Our writer, Nick, filmed a lot of footage of his meetings with Delia, which I had access to. I did meet her very briefly during filming, but only because she wanted to visit the set and of course I was respectful of that.

"I didn’t do lots of research into abusive relationships either, instead I just focussed on the character, on who she was, how she responded to things, and what I could gauge about how she interacted with people."

"Then you go from there and you try to be as accurate as you can in terms of how that person would behave and respond."

Filming such dark scenes was tough for Anna, although she felt "embarassed" to admit it as she was able to switch off after filming.

"It's not like doing a 12-hour shift as a nurse, so I get embarrassed to say that," she explained.

"It’s not a nice headspace to be in, but of course I get to step away from it. You have to keep a firm grip on the fact that it is not your reality – very sadly it was someone else’s reality and it was really difficult for her."

She added: "It affects you a little bit in the day, you wouldn’t be doing your job properly if it didn’t, but then you’ve got to get a firm grip on yourself, go home and be very thankful that you’re not actually living any of those things."

Anna said it was crucial the series was told from Delia's perspective as she wanted to show how resilient she was.

She was keen to celebrate Delia's bravery and individuality rather than "showing more gratuitous violence against females on TV".

"I didn’t really want to focus on the abuse. We’re getting inside the mind of a woman who went through a lot of very complex things, not just to do with John Sweeney, and I’m very proud of the drama," she explained.

The actress was also eager to highlight the issues Delia faced with the judicial system and how she maintained her strength throughout.

Until I Kill You is available to watch on ITVX