David Duchovny says he and Gillian Anderson "both went a little nuts" thanks to The X-Files

“At times we were nuts with one another, where she [Anderson] was acting crazy or I was acting crazy, or we were both acting crazy. But the thing about being crazy is you don’t know you’re crazy. I look back now and say, ‘Oh, I was a little nuts.’ And I think Gillian would say the same. We both appreciate why the other was crazy. We get it, and forgive.”

Duchovny also finds the third “star” of The X-Files – the show’s conspiracy theories – a little crazy to deal with. "People can't keep secrets," he declares. "I've never known anybody, not one person, to keep a secret. I find it hard to believe that they're keeping aliens from us because it's pretty juicy. You come home from work and you go, 'Honey, I've got to tell you something but you've got to promise not to tell anyone. They're here! I saw an alien today.’ She’s like, ‘I won’t tell anybody.’ And is then straight on the phone to her mom. That was my problem with JFK. There was no way. If there was a conspiracy to kill the president, somebody talks. Somebody along the way opens their mouth. There are too many people, too many secrets to keep. It’s not human nature. I don’t believe in it.”

Audiences last saw Mulder and Scully in the 2008 feature film The X-Files: I Want to Believe — but the storyline received mixed reviews from critics and a third movie was canned. However, Duchovny promises a return to form for the new six-part TV series, premiering on Channel 5 this week.

“The X-Files is very flexible and malleable in that we’ve got many genres within the show,” he says. “There’s the horror X-Files. There’s the thriller X-Files. The mythology X-Files. A romantic element creeps in every now and then – and then there’s the comedic X-Files. In the second episode [of the new run], Mulder is a complete goof. He’s always losing his gun and falling over. He’s always turning the wrong way when something is happening. It’s not the same guy as the heroic Mulder in the first episode.”

Early on in The X-Files, Mulder was revealed as an Oxford graduate — and, just like his character, Duchovny is well-educated. Born in New York in 1960, he went to school in Manhattan before he went to Princeton University, where he was rewarded a BA in English Literature in 1982. Soon after, he went to Yale to obtain an MA — although his PhD work remains unfinished; seemingly abandoned in order to pursue an acting career. His father was a writer and publicist and his mother was a teacher originally from Aberdeen, although his family history also has roots in Poland and Ukraine.

Despite a high-profile relationship with Hollywood actress Téa Leoni – they wed in 1997 – Duchovny’s profile dipped in the UK after The X-Files. While Gillian Anderson enjoyed success in a string of literary adaptations on BBC1 (Bleak House, Great Expectations), he spent most of his time working on lesser-known movie projects – although he eventually returned to the TV spotlight in 2007 with the eyebrow-raising comedy Californication.

It saw Duchovny tackle the raunchy – often naked – role of sex-obsessed author Hank Moody. The US show won rave reviews and bagged him a Golden Globe but was a drastic change from the family-friendly sci-fi hit that had made him a household name. “In some ways, I was reacting against The X-Files,” the 55-year-old laments. “I wanted to do a comedy and saw the pilot script of Californication. I thought, ‘I can do that.’ ”

The scandalous character and salacious storylines spun many heads in Hollywood – but when Californication creator Tom Kapinos first came up with the story of the alcohol-swilling, drug-taking womaniser, Duchovny wasn’t on his mind. “I didn’t think about anyone,” Kapinos admits. “I just wrote it as a writing sample, and had fun with it. But when we got picked up, there was a shortlist and, of course, David was at the top for me. There are so few guys who can actually pull this off; be charming and funny and good-looking. Girls love him and men don’t begrudge him that.”

After the first series of Californication finished in the US, tabloid stories speculated that Duchovny’s relationship with Leoni was on the rocks, and in 2008 – as if emulating a script from his show – the actor confirmed he’d entered a rehabilitation centre. “I have voluntarily entered a facility for the treatment of sex addiction,” he said in a statement released through his lawyer. “I ask for respect and privacy for my wife and children as we deal with this situation as a family.”

The tabloids commented that life was imitating art, but Duchovny put on a brave face. On television, the show soared and continued for seven successful years – but behind closed doors, Duchovny’s marriage came to an end in 2014 when the pair filed for divorce.

The two actors remain committed to their children: 13-year-old Kyd and 16-year-old Madelaine. Both teenagers visited Duchovny on the Vancouver set of Channel 5’s sci-fi reboot. “They’re happy about The X-Files because they’ve heard so much about it, but they didn’t really have any personal experience with it,” says the proud father. “My son has seen quite a few episodes, but my daughter is into Game of Thrones and I kept telling her, ‘We’re just as good as they are.’ I took her boyfriend on set with me every day because he wants to learn about film-making. I got him enlisted in the project.”

Duchovny is also working on the second series of the Charles Manson-inspired crime drama Aquarius – but admits that at the start of his career he never imagined he’d be in such a successful and lucrative position. “When I was younger, I never looked ahead. No, I just wanted ‘a pot to p*** in’, as my mum would say. I was always afraid that I’d end up in the gutter. That was our fear growing up; not to have any money and to end up homeless.”

He pauses before adding: “I mean, it wasn’t like that was imminent – but my mother was born during the Depression in Scotland and it was different. Just to have a place to live and food to eat was enough, which was a good attitude to have.

“I always wanted to be engaged, creative and imaginative – and to not have to go into an office every day. That was the life that I wanted. I didn’t want to wear a suit and tie, which is the f*****-up thing about having to play Mulder again. When I went in to work, I had to wear a suit and tie. It happened with Aquarius, too, so I’ve really screwed myself. I’ve got two shows where I have to wear a suit and a tie, which is what I didn’t want to do with my life – but there you go.”