There’s a new Doctor in the house – but what’s he doing with Queen Victoria? Ahead of the new series materialising this Saturday, we went behind the scenes for a glimpse at the future. By Peter Ross

IMAGINE, if you will, that you can travel through time. Instead of witnessing the last days of Sodom and Gomorrah or visiting a hideous future where King Pete and Queen Kate are celebrating their golden jubilee, let’s go back just a little, to October 6, 2005. The place: a narrow corridor in a television studio in Wales. A red light above the door ahead blinks off, and a man walks through. He’s dressed as a Scottish soldier from the Victorian era, and while kindly holding the door open for me, is checking the messages on his mobile phone.

Such anachronisms go with the territory when you are filming Doctor Who. This TV studio in Cardiff is the crucible from which the series emerged in March 2005 after a nine-year hiatus. Starring Christopher Eccleston and Billie Piper, and reworked by Queer As Folk writer Russell T Davies, it was wildly successful, both creatively and commercially. When the Scottish actor David Tennant made his debut in the role on Christmas Day 2005, only EastEnders did better in the ratings; Doctor Who has invaded the mainstream and ruthlessly taken it over.

On-set in Cardiff, Tennant is nervous energy personified. While waiting to film a scene, he jumps up and down on the spot and waggles his fingers, then attempts the dance routine from the latest Rachel Stevens video. Today, they are filming the second episode of the new series – Tooth And Claw, which is set in the Scottish Highlands. In it, Queen Victoria’s train derails and she seeks shelter in the mansion of a former friend of Prince Albert’s. Unfortunately, the grand country pile has another house guest – a werewolf. The Doctor and his travelling companion Rose are around too, a Tardis malfunction seeing them fetch up in 1879 when they were actually attempting to attend an Ian Dury gig in 1979.

“It’s a bit confusing today,” says Tennant, while waiting for the cameras to roll. “Lots of running up and down corridors. You tend to forget which you are in. But it’s a Doctor Who tradition, running up and down corridors.”

He’s wearing the brown pinstripe suit that is his Doctor Who outfit (“Jarvis Cocker had this look 10 years ago”), and leaning up against the scenery. There’s a deer skull screwed to the wall above him, and a candelabra nearby. One woman has the job of keeping the candles lit, which is bad news for Billie Piper – Rose in the show – who sets her hair on fire while running past, but quickly pats it out. “I’ve got so much hairspray on as well!” she cackles, clearly amused. She walks around, getting the cast and crew to smell her singed locks. “Mmm,” says Pauline Collins, who is playing Queen Victoria. “I love the smell of burning hair.”

Such incidents offer much-needed excitement on-set. While it’s thrilling to watch, Doctor Who is gruelling to make. Filming began on this new series in July 2005 and continued until the end of March. Cast and crew work 12-hour days, and much of today is taken up with simply running up the corridor towards the camera. There isn’t even a werewolf chasing them. That’s a special effect which will be put in later. In the meantime, to give the computer animators a guide to work towards, the cast are pursued by a man in body-hugging white Lycra, complete with hood. He looks exactly like one of the sperms from Woody Allen’s film Everything You Wanted To Know About Sex But Were Afraid To Ask.

During a break in filming, David Tennant sits down with a cup of tea to talk about starring in Doctor Who. He has been a fan since he was a child growing up in Renfrewshire and is one of those people who know more about the show than is strictly healthy (his earliest memory is of seeing Jon Pertwee regenerate into Tom Baker), so to actually become his boyhood hero has been rather overwhelming.

“It’s a bit surreal,” he nods. “It doesn’t seem plausible that you should suddenly get your own Tardis. It seemed fantastically unlikely when they asked me to do it. I just laughed.”

When Christopher Eccleston agreed to play the Doctor it was a leap of faith – one of Britain’s most serious actors opting to portray a character who had become a kitschy, culty joke, smelling of cheese and mothballs. Tennant, on the other hand, faces a different kind of pressure – meeting the high standard set by his predecessor.

“I owe Chris a lot because he was part of creating a phenomenon last year, and his very presence gave the show a mark of quality which some people didn’t expect,” he says. “My problem is I have to live up to that and not be the reason that this year it falls to bits. So it’s not so much a leap of faith for me as a leap of hope. I’ve got much further to fall now that the show is such a big hit. It is intimidating. You think, ‘What if I’m the George Lazenby of this?’ But then you think, ‘I can’t not take it on.’”

Russell T Davies insists Tennant was their number one choice for the role. Davies has worked with him before, when he played the famous philanderer in Casanova, and this, together with his roles in Blackpool (cop has affair with chief suspect’s missus) and Secret Smile (psychopath seeks revenge on ex-girlfriend by dating her sister), gives him an air of unpredictability which creates a nice tension with his boyish charm .

“There is an essential Doctorishness to who [the character] is,” says Tennant. “It’s a moral certainty, it’s a humanitarian, egalitarian fairness. It’s a slightly anti-authoritarian, anarchic way of doing things. He’s a loner, a free-thinker, and also a bit of a kid. He’s got the exuberance of a child combined with the mental ice of a 900-year-old from a race that control the fabric of time. But at the same time, because there are all those elements, it’s everything and nothing. He’s a bit of a blank canvas as well.”

At this point we have to stop talking. The director – Euros Lyn – has called for quiet on set. They are going to film the werewolf transformation scene. Tom Smith, the actor who will become the werewolf, stands to one side of the camera, doing stretching exercises. He is bare-chested and wearing special contact lenses to make his eyes entirely black.

“What I’m really looking for from you in this shot,” explains Lyn, “is that ecstatic feeling you’re getting from the moonlight filling you with everything you ever yearned for.”

Smith nods , they shoot the scene. He twists and jerks about, the veins of his neck sticking out, making gigantic phlegmy noises and showing teeth made up to look scummy and rotten. It’s fairly disturbing even in these artificial circumstances. God knows what it will be like on screen.

“Brilliant!” says Tennant when it ends.

“I hope we get letters by the bucketload,” says producer Phil Collinson, rubbing his hands.

“This is supposed to be a kids’ show,” someone jokes.

“Yeah, scare them shitless,” Tennant laughs. “That is very much what we want.”

According to Davies, they are very careful about the levels of fear and horror in a show which goes out on Saturday evening and is supposed to be family entertainment. “There’s no blood,” he says. “There’s absolutely no tooth-on-skin contact. You do not see any flesh being thrown about the place. And our werewolf has been visible on BBC1 trailers, so it’s not coming at you out the blue. This is as scary as we get, but we are absolutely within the guidelines. There is absolutely no kudos in pushing the boundaries, because the last thing I want is for people to switch off.”

Anyway, there are worse things on mainstream TV, he insists. “What pisses me off is in EastEnders, the Mitchell brothers – who would punch me in the face – are glorified as heroes. We are asked to admire two bastard thugs.”

In fact, by far the most disturbing moment of the previous series of Doctor Who was the least grisly – The Empty Child, a two-parter in which the gas mask-wearing ghost of a little boy killed in the Blitz haunts his gymslip mother. Something of its skin-crawling spirit looks to have been captured in New Earth, the first episode of the new series, in which a cats dressed as nuns seek antidotes to diseases by testing them on captive humans.

Written by Davies, the episode is a spin on MRSA and animal vivisection (with un-intentional shades of the recent drugs-trial horror) and demonstrates his alchemical knack for turning headlines into plot lines. Under his influence, Doctor Who has become enjoyably liberal, featuring an inter-racial relationship and an alien whose extreme horniness has no regard for gender or indeed species.

“One of the great pleasures of the first series is that we did manage to do that at seven o’clock on a Saturday night and nobody batted an eyelid,” says Phil Collinson . “Five years ago, if we’d put a bisexual character in a series that has a huge children’s following there would have been a massive storm of protest, and I think it is a genuine reflection of our times that that is not the case now. As a society we are more liberal and accepting, and I think what Russell’s writing does brilliantly is reflect real life. Even though this is science fiction, we are dealing with real people with real emotions.”

When I speak to Davies, he agrees that for all the special effects and scary monsters, the pain and pleasure of human relationships is right at the centre of Doctor Who.“That beating heart,” he says, “is always there.”

Flash forward through time now to April 6, 2006. The place: the Centre for Contemporary Arts in Glasgow. Tennant, Piper and Davies have come to the city to screen Tooth And Claw (the transformation scene turns out to be really quite frightening, but there’s a funny Balamory reference elsewhere to even things up) and meet the press.

During a question and answer session we learn the following: (a) Davies hates the Royal Family – “As soon as Doctor Who replaces the Queen’s speech on Christmas Day, the better this country will be”; (b) Piper doesn’t mind meeting fans, with one caveat – “The only time it really annoys me is when I’m smoking a fag, because when a kid walks up I always feel obliged to put it out. I can never bloody finish a cigarette”; (c) Tennant recently appeared on Ready Steady Cook – “The tensest 20 minutes of my life; I’m trying to chop tomatoes and Ainsley wants to talk about Daleks!”

I manage to get a little time with Tennant on his own. In the five months since our last meeting he has become one of Britain’s best known – and most desired – actors but he’s buzzing with excitement about the show. “I knew Doctor Who was going to be crazy, relentless and bizarre, and it has been all those things times 10,” he says. “But it’s great fun because every day feels so extraordinary.”

There’s a lot of laughter on-set, and plenty of tears too; Tennant says he is “personally invested” in the character and, as the Doctor is an alien with two hearts, I suppose it makes sense that the man playing him should find it an emotional and passionate experience. “I’m aware,” he grins, all teeth, no claws, “that I am in something that I will be proud of for the rest of my life.”

The second series of Doctor Who begins on BBC1, April 16, 7pm. Tooth And Claw is broadcast on April 23.