‘ I’m g I’d h smug

But actor David Tennant admits he already had an interest in the sick murderer – because people said they looked alike.

And it has to be said, with the oversized glasses and sideparted hair, the resemblance is uncanny.

Years before being cast as Nilsen, Tennant had read his biography, Killing For Company, and had lived near the scene of his later murders, Cranley Gardens in north London.

Tennant says: “It was a story that was on my radar. I’d read Killing For Company many years before, partly because I lived just down the road from Cranley Gardens so it felt like a bit of local history, and also because a couple of people had said, ‘ He looks a bit like you’.

“Then you start investigating this story. It was a story I thought we should tell.”

The three- part show, Des, looks at Nilsen’s arrest after human remains were found in his drains by a Dyno- Rod plumber who called police.

Remains

The monster killed 12 men and boys and tried to murder seven others between 1978 and 1983. Nilsen plied his victims with alcohol and lured them back to his flat, before killing them, often using strangulation, chopping up their bodies and keeping the remains.

When he was arrested he claimed to have murdered 15 but insisted he couldn’t remember their names, meaning police struggled to identify the victims, who were often homeless.

Tennant says: “I was 12 when he was arrested so it was a name I was aware of. I knew he was a bogeyman from the 1980s.

“It’s taken about five years from when we started talking about it to getting it on screen and I feel very privileged to have seen it through.”

The Scottish actor, who previously starred in Broadchurch and Doctor Who, was also keen to understand Nilsen as much as possible and not end up simply doing an impression of him.

He says: “There is some footage you can watch, there’s a lot that has been written about him and people who knew him quite well. I did spend quite a lot of time studying him, listening to his voice. You take all that in and then forget about it. You don’t want to be doing a Rory Bremner version of Dennis Nilsen – you are trying to get to the truth.

“From an acting point of view, these are the sort of psychologies you are fascinated by. It doesn’t mean you agree with them or you commend them, but trying to unpick what went on in the mind of someone like that is horrifying and fascinating.”

Yet despite all his research, Tennant is still at a loss as to why Nilsen committed his horrendous crimes.

“I don’t think Dennis always