Stylist: What was it that captured your attention about this particular drama?

Niamh: It was a unique perspective that this woman had on this case and that I was not aware of. I was familiar with the Rachel Nickell murder, but I wasn’t aware of the woman who was placed undercover. I had so much admiration for Sadie, and women in that job: the bravery of doing undercover work, the situations in which they would have to go. That strength she imbues in the character was very unique and something I hadn’t seen portrayed before.

It’s not often we see cases like this through the eyes of a woman, rather than the perpetrator of the crime. What’s the significance of that?

It was really important for a story like this to be told from the perspective of Sadie’s character. I think, for a woman in the early 90s, in this job, she’s very much a woman in a man’s world, trying to hold her own in a situation where she has to be both vulnerable and strong at the same time. You have to show the vulnerability of a character in order for the audience to see how exposed she was: she went to meet who she thought was Rachel’s killer, unarmed.

We chose with this character that she would be very isolated: she is incredibly lonely and it was important to show how that might have an emotional effect on a person. For me playing this character, especially during the lockdown, every night [after filming] I would have to sit with the day and digest the scenes and emotions.

I spoke to a few officers who have done this job to get a sense of how those women dealt with everyday life doing a job like this – I didn’t speak directly with Sadie, to protect her identity. One said to me: you create your character, but while for you, as an actor, if you mess up the line, you get to go again. If I mess up my line, I could end up getting hurt. That put goosebumps on my arm, about how brave these women were.

Deceit: Niamh Algar, the star of Channel 4’s new true crime series, on making the honeytrap drama