Life will never be the same again for Matt Smith. Twelve months ago, the Northampton-born actor could drink anonymously in any London pub. But since eight million people in Britain watched his debut as the 11th incarnation of the BBC's famous Time Lord over Easter, he has become one of the nation's most ubiquitous television stars.

Two weeks before, speaking to the world press after The Eleventh Hour, the first episode of the fifth season, was premiered at a Cardiff cinema, he seemed to be taking it all in his gangly stride.

"Hopefully no tomatoes will be thrown at us in the street," he said. "I hope people will respond to it. They will maybe find some new things that will excite them. But hopefully they will enjoy it because we've got a brilliant journey that we're going to take you on."

Following in the footsteps of David Tennant, Smith has a lot to live up to. During his five-year stint, the Scot became the most popular Doctor since the science fiction series was first broadcast in 1963 with William Hartnell in the title role.

Six Doctors later, dwindling audiences contributed to its unceremonious cancellation in 1989. And after Paul McGann starred in a disastrous 1996 American co-produced television pilot, it appeared to be dead and buried for good. Consequently, expectations weren't high when Russell T. Davies resurrected it in 2005 with Christopher Eccleston at the helm of the Tardis.

However, it proved to be an overnight sensation, regularly topping the ratings and winning numerous accolades. Eccleston departed at the end of the first season and Tennant replaced him for the 2006 Christmas Special.

After Tennant resigned in a message broadcast at the 2008 National Television Awards, months of feverish speculation ensued about the identity of his successor. The likes of James Nesbitt and David Morrissey were linked to the vacancy before behind-the-scenes documentary Doctor Who Confidential announced Smith's surprise appointment last year.

Smith soon became the subject of much criticism. Not just because he was almost completely unknown — he had previously only been seen in political comedy Party Animals, Philip Pullman-adaptation Ruby in the Smoke and race crime drama Moses Jones — but because of his relative youth.

At 27, he is two years younger than Peter Davison when he took over from Tom Baker in 1981. Steven Moffat, who has replaced Russell T. Davies as head writer, believed that only an older actor could possess the necessary gravitas to play time and space's elder statesman.

"I thought they would have to be in their mid-30s to mid-40s," he says. "I still maintain that's where most of your Doctors will be, in that age group; young enough to run, but old enough to look like they can be king of the universe."

According to executive producer Piers Wenger, Smith stood out from his very first audition. "We knew he was the one," he says. "It was abundantly clear that he had that 'Doctor-ness' about him. You are either the Doctor or you're not."

While Smith embodies the maverick spirit of the character, he didn't grow up watching the show from behind the sofa like so many children of the previous three decades.

"I was part of that barren spell when kids weren't given the joy of Doctor Who because it wasn't on television back then," he recalls. "But I was very aware of it. In England, it's ingrained into our fibre so it's impossible not to be."

He has now done his homework and cites Patrick Troughton as his favourite predecessor, having watched the second Doctor's 1967 inaugural storyline Tomb of the Cybermen more than 20 times.

"I became obsessed with him," Smith says. "Once you start to engage with it, you can't stop. Each month you've got a completely new story and brilliant new supporting actors coming in. But in terms of trying to emulate anything, you have to carve out your own path. There may be shades of past Doctors in there but it's never been conscious."

Smith was also instrumental in the choice of the Doctor's new outfit, choosing to wear a bow tie with a tweed jacket, rolled-up trousers and black boots, a decision that led one journalist to cruelly describe his look as "one part librarian, one part member of [boy band] JLS". Moffat was more accurate when he suggested that the Doctor is "a totally inappropriately dressed man who probably thinks he's cooler than he is".

"I had a very active role in that at various stages of development," says Smith. "It feels like my identity. It has to reflect your personality. But this Doctor's costume will constantly evolve and it will vary."

He also establishes an immediate rapport with his new companion Amy Pond (Karen Gillan), whom he first meets in an unexpected fashion at the beginning of The Eleventh Hour.

"We're a real team," he declares. "We're very fond of each other. It's something that we had to work out how to play on screen. What I find most particular about making this show is the tone. If the tone is really off or on, you're very much aware of it."

Like Smith, 21-year-old Gillan was not previously an ardent fan of the show. In her case, though, it was more of an advantage.

"Steven Moffat told me to remember that Amy has never seen Doctor Who so she questions everything," says the Inverness-born actress. "The companion asks so many questions so the Doctor can then explain it. So you have to find new ways to ask those questions and I have to put some emotion into it. It was an interesting thing for Steven to say because it gave me the scope to be completely fascinated by Doctor Who."

Gillan was impressed by the diversity of the new series, which sees Amy and the Doctor teaming up with Winston Churchill in episode three's Victory of the Daleks and meeting Vincent Van Gogh in the ninth episode, which was written by Richard Curtis and stars Bill Nighy. They will also encounter the Cybermen and the reptilian Silurians, who were last seen in 1984's Warriors of the Deep.

"You're going to so many extremes in every episode," she says. "You're facing death-defying situations every time and that's fun. You have to find new ways of creating that kind of feeling, which is a challenge."

Even though his tenure is still in its early days, Smith has already been asked how long he intends to stay on as the Time Lord. However, he has no plans to quit just yet and isn't worried about being typecast.

"David Tennant did extraordinary work around the role and, if anything, it sets extraordinary opportunities to do more varied work," he says. "I would absolutely love to continue being the Doctor. It's a role I enjoy very much. To my mind, it's the greatest part there is in this country and I'm very fortunate to have it."

* Season five of Doctor Who plays on Prime next month. Doctor Who's Greatest Moments screens next Sunday at 10pm.