All that Californicating seems to have left David Duchovny happy to return to The X Files, says JEFF DAWSON

Deep in the bowels of a disused mental institution, a cadre of nuns shuffles down the corridor. This crumbling Victorian edifice on the outskirts of Vancouver - atmospherically chilled and, at 3am, Exorcist-eerie - has been dressed as the Our Lady of Sorrows Catholic Hospital, a key night-shoot location for the film The X-Files: I Want to Believe.

“They’re not real nuns. I hope not,” quips David Duchovny, who is reprising his role as the FBI agent Fox Mulder. The wry grin says it all. Recently, before being pressed back into service in this new, feature-length spin-off from the six-years-dormant television series, Duchovny has enjoyed second-wind success in the libertine drama Californication. As Hank Moody, a washed-up LA writer and comically priapic midlifer, he had, in the very first episode, been accorded a special kind of devotion by a bride of Christ. The act drew predictable howls about sacrilege from conservative quarters. “I heard that, in Australia, there were some problems,” he says dismissively, typically deadpan. “But they’ve got to take it on the lips like everybody else.”

I wonder whether Duchovny’s reinvention as a compulsive copulator might be upping the level of expectation, this time round, for closer encounters between Mulder and Dana Scully (Gillian Anderson) - not all that unrequited, chaste stuff that characterised much of their television relationship. Even when the pair did eventually and enigmatically get it on, somewhere in the later stages of The X Files, they had to complicate things by spawning some kind of mutant sprog with paranormal powers, swiftly given up for adoption.

“Who knows?” he shrugs. “As a viewer of other actors, when I go into a film I don’t hold their other work up against them.” He is kidding himself here - as a slew of self-mocking cameos in everything from The Simpsons to Zoolander attests. If Duchovny were to be hit by a bus tomorrow (or, God forbid, abducted by aliens), it is unlikely the headline writers would desist from referring to him as anything other than the star of The X Files or, in the light of all that Californicating, The Sex Files. He concedes the point: “I’m not complaining. If I had to be associated with a TV character, you know, I’m happy that it’s those guys.”

With a quick, dry wit (Yale via Princeton and an elite Manhattan prep school, where he was a classmate of JFK Jr), Duchovny is a likeable sort. On the cusp of 48, he is wearing well, attributable to a strict diet, yoga and, it would appear, a just sub-Paul McCartney dollop of hair dye - all part of looking presentable if you’re going to have your backside in people’s living rooms every week. The most endearing thing about him is the perma-smirk plastered across his chops, which suggests, even at this ungodly hour, that what he really wants to do is drag you to one side and confide that this acting lark’s a load of old crock. “You know, action scenes and sex scenes are pretty silly, because you’re just faking,” he whispers. “Of course, everything in the movies is fake, but they’re even more fake.”

You can forgive the nonchalance. Several years into his career, back in the early 1990s, Duchovny had begun to accept his lot as a journeyman thesp. He was better known as a Clist lothario, a string of relationships with Hollywood lovelies including Winona Ryder and Sheryl Lee complemented by his continuing part as the narrator in the soft-porn television knees-up Red Shoe Diaries. He’s still an object of lustful attention. The indie songstress Bree Sharp penned a swooning valentine to him (“David Duchovny, why won’t you love me?”), which still racks up hits on YouTube. Dare one mention internet postings celebrating an early X Files episode in which he sports budgie-smuggler Speedos?

Fair play to Duchovny, he has always gone along with the joke, most notably in The Larry Sanders Show, where he had a recurring role as a guest with a man-love yen for Garry Shandling’s discomfited chat-show host. There was, too, the Steven Soderbergh movie Full Frontal, in which Duchovny petitioned for a $500 “extra” from a hard-up masseuse. But it is all tangential. In 1993 came The X Files, the little green men, the mysterious cigar-shaped objects and everything else. One minute, he was in a niche sci-fi pilot, a perceived leg-up to a few decent film roles; the next, that UFO-infatuated drama had exploded into one of the most successful television shows of all time, The Twilight Zone for a new generation. It was bigger than the Beatles, he joshed. Duchovny had sealed his place in showbiz history.

As “Spooky” Mulder, the conspiracy-obsessed believer to Scully’s sceptic, he romped through most of the 200+ episodes, beating off supernatural forces and assorted monsters, indulging the central conceit that the American government is involved in a cover-up about extraterrestrials. In 1998 came a first film, The X Files Movie, since rebranded The X Files: Fight the Future. (Titles, evidently, are not the producers’ strongest suit.) It was a big hit.

At the franchise’s peak, however, Duchovny seemed to bite the hand that fed him. After the fifth season, tired of the relentless schedule of 10-months-a-year filming in Canada, he made the show relocate to LA to afford him time with his new bride, the actress Téa Leoni. Die-hard X-philes howled at the change in the feel of the programme, which had previously aped the drizzly forest atmospherics of the similarly Pacific Northwestern Twin Peaks. Duchovny had graced that show, too, as an FBI agent, albeit a cross-dressing one, an indicator of where his career had been heading.

Having destroyed a local industry, Duchovny then sued for $25m over royalties. Chris Carter, the snow-haired surfer dude who created the series and is back behind the camera for the new film, treads diplomatically round this. “The problem is, when you get successful, money enters the equation. And money changes everything, as the song lyric goes.” After the seventh series, a seemingly bored Duchovny opted out, ceding the legwork of the last two seasons to Anderson and incoming agents Doggett and Reyes (Robert Patrick and Annabeth Gish), and appearing only sporadically. He did return for the underwhelming and strangely spiritual 2002 finale, which concluded with Mulder and Scully as fugitives, the point at which the new film picks up.

“Whatever disillusionment I had... disillusioned is the wrong word,” he says. “It was more like creative fatigue – not with the characters, franchise, Chris, Gillian or whomever, never anything like that.” He cites simply how a five-year gig became a six-year one, then seven, then eight. “There was always this receding finish line. At some point, I realised there was never gonna be a finish line unless I finished it for myself.”

Duchovny retreated to Malibu, raised a family and tried his hand at the odd film, either acting (Things We Lost in the Fire) or directing (House of D), but nothing had a fraction of the impact - until Californication, which this January won him a Golden Globe. The second series was recently rocked by the untimely death of the husband of co-star Natascha McElhone, but is set to return to our screens later this year.

Why, though, after all this time seeking a new direction, has he jumped back into The X Files? Especially as the new film is being shot in Vancouver, where the local media had conducted the equivalent of burning his effigy in the street. “To come back to it is not to go against any feeling I ever had,” he says. “It was only a case of, ‘I need to get away from this for a little while, if only to find out what I want to do.’” It was not a contractual obligation. “My desire in envisioning how I would get off the series was, ‘Let’s stop working so hard, let’s turn this into a movie franchise.’” More films are promised, though they had better be quick: according to the show’s “mytharc” (The X Files is cultish enough to have its own vernacular), the world will end in 2012, which doesn’t augur well for the London Olympics.

Making an X Files film this time around would seem a bigger risk without a television series to feed off. But, says Duchovny, this will assure it a greater cinematic worth. “My one stipulation was that it should be stand-alone. On the first movie, even though we went around doing press saying you didn’t have to know the TV show, that was pretty much a lie.” Mulder and Scully will need to be reintroduced, but Carter has done a good job, Duchovny stresses, of “setting up their points of view, yet not belabouring it so much you’ll go, ‘We already know all this crap’”.

A key factor is that, 15 years since Duchovny first suited up as Mulder, life has moved on for the agent. “If I try to play him exactly the same way, it would be like a 50-year-old stripper getting up there,” he sniggers. Mulder is still a man obsessed - “That’s what makes him a great hero, the fact he doesn’t stop searching,” - though for what, these days, is unclear, such is the three-line whip laid down by the producers, which renders discussion of the plot verboten. Such is the paranoia, the production office has set up its own ministry of misinformation, feeding false story lines to the internet. Only a few coded copies of the full script are in existence, all locked up in a safe at night. “I keep mine lying around,” Duchovny adds drolly.

Unless it is all an elaborate hoax - and how X Files if that were so - what has been witnessed would suggest a plot concerning demonic possession, with Billy Connolly as some kind of seer guiding the Feds. “A thriller in the tradition of The Silence of the Lambs,” Duchovny says, “A fun action movie.” The truth, you might say, is out there.

It is not just Mulder who has changed, of course, but the world. Not so long ago, the prospect of shadowy global networks and a new world order seemed a jolly dramatic wheeze, tapping into premillennial angst. A March 2001 episode of The Lone Gunmen, a short-lived X Files sister show, even had the American government deliberately crashing a passenger jet into New York City to propagate fear and strengthen its own hand. Post-9/11, such things seem facile. But Duchovny insists that we still need men like Mulder to ask big questions.

“He is the guy who’ll speak truth to the power,” the actor insists - no matter what the circumstances. Though it probably explains why the film is sticking to a fantasy theme.

So, does he, Duchovny, believe in, you know, Area 51, the flying saucers? “It seems unlikely we’re alone in the universe,” he muses. “Yet I’m fairly certain nobody’s hiding any contact we’ve had. The idea that the government could withhold that kind of information when they can’t even get gay sex in a bathroom without being followed [a reference to the Republican senator Larry Craig, copped last year]...”

Fans may insist otherwise. One should never underestimate the zeal of the sci-fi devotee. I’m reminded of a story about Tom Baker, who, some years ago, attended a Doctor Who convention at which he strode onto the stage to be greeted by an audience that rose as one, chanting: “Take us with you.” Duchovny must get that sort of stuff all the time. He gives one of his trademark smirks: “Yeah. Even more now with Californication.”