EVEN before making her debut on the screen in TV’s longest running sci-fi show, Pearl Mackie already had her sights set on her next big screen role.

“I’d quite like to play James Bond.”

The relatively unknown 29-year-old is appearing in the new series of BBC One's Doctor Who as the Time Lord’s companion Bill Potts. As if having millions of devoted fans – known as Whovians – isn’t enough to contend with, she has also been cast as the show’s first openly gay Tardis traveller.

But Mackie noted: “It shouldn’t be a big deal in the 21st century. It’s about time isn’t it?”

Far more controversial, it seems, is the admission in a recent Radio Times interview that, unlike the current Doctor Peter Capaldi, she hasn’t been a particular fan of the cult series – because it wasn't being screened for much of her childhood.

“It came back in 2005 when I was about 16 and going out at the weekends,” she said. “I’d seen bits – I’d seen the Daleks on the hundred scariest moments on TV and stuff like that. But I didn’t really know the show like a fan would.”

Which might explain why she was stumped by the question of what type of power fuels the Tardis during an interview on The One Show, triggering a 'furious' reaction on Twitter, according to some newspaper reports.

While she hazarded a perfectly reasonable guess of "space engine oil", any respectable Whovian knows the answer is of course artron energy, involving psychic traces which feed off the rift in space and time and which is found in the brains and bodies of Time Lords. Of course.

The role of the companion is a key part in Doctor Who time travelling adventures. But defining exactly which characters fall into that category is a more complicated affair than it would first appear. Do they have to have travelled in the Tardis? Or appeared in a minimum number of episodes? Does non-human robot dog K9 count as a companion?

There is no official list kept by the BBC, but from a quick scan of various listings it appears Bill will be the 44th companion to the Twelfth Doctor. Or thereabouts.

In the first episode she is introduced as a canteen assistant at St Luke’s University in Bristol, where she serves chips to students and nothing ever happens – until the Doctor turns up.

Mackie describes her character as “quite direct” with a tendency to surprise the Doctor, while Capaldi told the Radio Times their on-screen relationship had an element of “Educating Rita”.

“The Doctor decides to take her on as a pupil and there’s a lot of jousting between them," he said. "They banter, for want of a better word.”

The level of interest – or to put it more bluntly, downright obsession – of Whovians is not to be underestimated. Mackie tells how within just a few hours of her casting being announced a fan had posted a selfie on social media dressed up as her. “I thought, ‘What on earth have I got myself into?'” she recalls.

It is undoubtedly the actor’s biggest role to date. Born in May 1987 in London, she studied drama at Bristol University before going on to the Bristol Old Vic Theatre School, which boasts a host of famous alumni including Brian Blessed, Olivia Colman, Naomie Harris and Jeremy Irons.

Her career began with a small part in 2013 British music comedy film Svengali and an appearance in the daytime soap Doctors, before she landed a role in the West End play The Curious Incident of the Dog in the Night-Time.

While she was appearing in that, her agent informed her of a new show called Mean Town. This turned out to be an anagram for Women Ten, a codename for the Doctor Who casting to prevent the casting directors being deluged with audition requests.

Mackie admitted she almost ran away from the meeting to read a scene with Capaldi at the Soho Hotel in London. "Just walking through the foyer was nerve-wracking," she said.

Steven Moffat, the executive producer and writer of Doctor Who, has spoken about how the decision to cast a mixed-race actor in the role was a deliberate choice – and that he had offered the part of the Doctor to a black actor before but it didn’t work out.

“We decided the new companion was going to be non-white,” he said. “It was an absolute decision because we need to do better on that.

"Young people watching have to know that they have a place in the future. That really matters. You have to care profoundly what children's shows in particular say about where you're going to be."

Mackie has also spoken of the importance of representing diversity with characters such as Bill on screen, which children and young people can identify with.

"It's important to say people are gay, people are black – there are also aliens in the world as well so watch out for them,” she said.

"I remember watching TV as a young, mixed race girl not seeing many people who looked like me, so I think being able to visually recognise yourself on screen is important."

She continues, "[Being gay] is not the main thing that defines her character – it's something that's part of her and something that she's very happy and very comfortable with."

But before she even appeared in an episode there has already been speculation over the future of Bill. Moffat is due to step down from the show after this year’s Christmas special and will be replaced by Chris Chibnall, who created Broadchurch.

This series is also Capaldi's final and there has been speculation that a brand-new companion will be brought in to go alongside the yet-to-be cast Thirteenth Doctor – with the question of whether a female will finally be taking over the controls of the Tardis.

For Mackie, there is no reason why female actors shouldn’t be taking on roles traditionally played by men. When it comes to her dream role of James Bond, she is insistent that she would not be playing ‘Jane Bond’.

"If I can be called Bill, I can be called James, can't I?” she said.