Daniel Mays used to wake up "screaming" because he thought serial killer Dennis Nilsen had locked him in an attic, before he even started filming ‘Des’.
The 42-year-old actor – who plays Detective Chief Inspector Peter Jay in the new three-part ITV drama – was haunted by nightmares about the real-life murderer, who killed at least 12 young men between 1978 and 1983 in north London by plying them with booze and then luring them back to his flat, where he would strangle them and cut up their bodies.
Reflecting on the work he put into the chilling show, Daniel told the Daily Mail newspaper’s Baz Bamigboye column: "I watched all these documentaries and pored over all this research…
"On two occasions I woke up my wife, Louise, screaming, because I thought I was locked in an attic with Dennis Nilsen."
The 42-year-old star admitted everyone involved with the show – including David Tennant, who plays Dennis – was determined to tell the story in the right way.
It means that while the murders are described graphically, they won’t be depicted on screen.
He explained: "It was always told from a point of respect."
David, 49, recently discussed the decision to take the attention away from Nilsen and instead focus on Jay – one of the first officers to come into contact with him on the day of his arrest – and Brian Masters (Jason Watkins), who interviewed the murderer on numerous occasions for the biography ‘Killing For Company’.
He said: "Because it’s a true story and because it’s also a relatively recent true story, there are still people alive who were affected by the horrific things that he did.
"You want to approach that responsibly. [Nilsen] worked in a job centre that you can visit. He lived in houses that still exist. His was just a very ordinary, humdrum life – apart from the fact that he murdered young men in his flat.
"By looking at these stories, you go, ‘How close am I to that? How much would it take to tip me into that world?’ Indeed, Dennis himself talked about, ‘Once you’ve done one murder, the next one isn’t so bad.’ "