Gillian Anderson revisits her role as one half of FBI duo Mulder and Scully in The X-Files: I Want To Believe.

While comic book geeks the world over are still glowing in the majesty of The Dark Knight, another cult favourite returns this month, in the shape of The X-Files and its own dynamic duo, Mulder and Scully.

Six years away from the world of alien invasions and the paranormal, everyone’s favourite FBI agents are back in business for their second big screen outing, The X-Files: I Want To Believe.

Ten years on from the first feature film, Fight The Future, creator Chris Carter has reunited the X-Files golden couple, David Duchovny and Gillian Anderson, heading a cast which also includes Amanda Peet, Billy Connolly and rapper/actor Xzibit.

For Anderson, who was paired with Robert Patrick for the last two seasons of the TV series after Duchovny’s departure, renewing the Mulder and Scully partnership was not a tough call to make:

“My decision to be on board was made a long time before the script was even written. I don’t know what I would have done if the script was bad, but fortunately I didn’t have to face that,” says the actress who turns 40 this week and is six months pregnant with her third child.

“We’d had the discussion early on, that were it ever to come to fruition, we’d all be on board for another film.

“With six years having passed when we’d been doing other things both professionally and personally, it felt like good timing.”

She adds: “You know, I wasn’t so much cocky about it but I was really confident that it was going to be really easy on the first day, and I wasn’t afraid at all. Usually I am terrified before I start something. And then for the first couple of days it sucked. It was horrible. I’ve spent such a long time trying not to do anything that even remotely resembled Scully whilst working, so when I was inviting her back again my brain was going ‘No, no, this isn’t supposed to be happening.’ And also we happened to start on the worst possible scene we could have started with.

“It was probably one of my most difficult days. It was a confrontation scene, I hadn’t even been ‘normal Scully’ before I had to be ‘upset Scully.’”

Since the final season of The X-Files was broadcast in 2002, Anderson has, like her co-star, been far from idle – roles in the BBC adaptation of Bleak House and films The Last King of Scotland and A Cock and Bull Story amongst her most recent work. She is also soon to be seen alongside Simon Pegg in How To Lose Friends And Alienate People, the film based on former Vanity Fair writer Toby Young’s hilarious memoirs.

She insists, however, that despite a desire to live in England and leave The X-Files behind, she has always left that particular door ajar:

“I think that I have always made it pretty clear no matter what has been rumoured at various times in the press, that were we to come together in order to do a film, that I would be happy and willing and hopefully able to participate, and so I just assumed, that it would just be a matter of time.

“There were a few times there when it looked like it might not happen but I was always on board.

“It was a formidable experience for all of us,” she adds.

“Even at the times when I was very outspoken about the challenges of the show, it was still something that I wouldn’t have changed for the world. I was always aware that this was something unique and valuable and precious and something that doesn’t happen very often and that we were all incredibly lucky. Coming back together again has been exciting. ”

While she won’t be drawn on whether fans will see any developments in Mulder and Scully’s ‘will they, won’t they?’ relationship, Anderson is quick to acknowledge the effortless on-screen chemistry she enjoys with Duchovny:

“The chemistry between David and I is something that is there naturally,” Gillian explains. “It has been there despite ourselves, no matter what moods we’re in or what was going on in our personal lives.

“No matter how we felt on a particular day – when we were in a scene together, the chemistry was there. There are shades of it in other projects I’ve done. But there’s something different with David and that’s the unexplainable bit.”

“It is great, it was great then too – it’s like a sibling relationship. It is just a natural relationship and now that we have grown up I think we are more appreciative of the relationship period and the unique experience that we have had together – and that we have an opportunity to continue and foster it. We have always loved each other and we are always going have the occasional battle.”

Gillian adds: “There are plenty of thrillers throughout history, but what makes the film unique is the particular kind of relationship, the intense relationship, between the two characters.

“It’s almost a marriage in a sense. Even though we’re not working side by side throughout the whole film, there’s that intensity between the characters and the thriller storyline at the same time.”

Originally brought in to supervise fellow agent Fox Mulder and his X-Files – weird and unexplained cases which he would often accredit to the paranormal while she aimed to explain scientifically – Scully has, says the actress, mellowed with time:

“I think she is more relaxed. I think she has made some choices in her life that have allowed her to do what she most wants to do, and that has mellowed her a little bit. She hasn’t lost any of her determination and passion about things by any stretch but she is mellowed a bit.

“I think what’s been important is to not have her change a lot. I think it’s important to show somebody that’s recognisable to the audience who is used to her. Obviously there has been a maturity that has taken place naturally.

“She developed and we all grew together. I think that her resilience and her strength, her intelligence and her determination was appealing for lots of young women. And apparently there is a whole new group of people out there who are discovering the show in reruns for the first time, which is awesome.”

* The X-Files: I Want To Believe is on general release now.