The show may be 47 years old, but the lead character is getting younger. Now piloting the Tardis through time and space is 27-year-old Matt Smith. Other than the his age, what noticeably sets Smith apart from the preceding 10 time lords is his thick mop of hair.

Hair has been a defining feature of many Doctor Whos: there was goldilocks Colin Baker, the grey professor look of John Pertwee, Christopher Eccleston's cropped Matrix do and the spikier, nightclub look of Smith's immediate predecessor, David Tennant.

Perhaps the Eleventh Doctor, with the point of his fringe falling sharply on his right eyebrow, is reviving the quiff - I ask whether it takes a long time to achieve his version of the 50's style:

"Oh it's something that comes completely naturally, actually. It does need a bit of a blowdry in the mornings but apart from that it's all completely instinctual for the old hair," he says.

The eloquent young Englishman is also bringing back tweed, another defining aspect of his character that he claims was a personal stamp.

"I do own a tweed blazer, which I actually wore to the first audition, would you believe it but I don't wear it any more because I think I would look a bit silly. But yes, I am a fan of tweed, I think it has an elegance and style, absolutely. An Englishness."

British papers have reported a spike in demand for Harris tweed since the new Doctor hit the airwaves. Whether or not there is a direct link, Smith thinks the fabric deserves a comeback.

While a somewhat gangly-looking Doctor may not exactly scream sex appeal, Smith brings it to the new series - especially when paired with wide-eyed, glossy-haired Scottish actress Karen Gillan, who plays his leggy companion.

She's Amy Pond, who was known as Amelia Pond before she started dressing up in saucy maid and policewoman costumes.

"She brings a great feistiness and a great sexiness. She's got real zest," Smith says. "I'm sort of slightly in love with Amy Pond."

And what is Smith's version of the heroic nerd?

"I think it's a bit bonkers and, hopefully, a bit reckless. Then I hope it's full of tragedy and sorrow and it's all the great things that the Doctor is, I hope to have all those colours."

Though Smith is of the generation that did not have a defining Dr Who as a child, other than the 1996 series featuring Paul McGann, he says that as someone growing up in Britain, it's always something you are culturally aware of.

He says it's not just because it now has its own computer game and fancy interactive website that the far-fetched story about about time-travel and magic continues to find a place on television:

"It's not bound by genre or space or time or logic, it's just limitless and completely infinite. Every few years it regenerates, so it moves with the times," he says.

"And at the heart of it you have a wonderful relationship about a mad hero who comes along and saves the day and travels around with an equally mad and brilliant companion. And I think there are so many stories that can be told in this idea."

Who: Matt Smith
What: The Eleventh Doctor, star of longstanding BBC series Doctor Who
When and where: Sunday, 7.30pm on Prime