Media playback is unsupported on your device Media caption Peter Capaldi discusses his take on the Doctor

Actor Peter Capaldi has promised that his Doctor will be "less user-friendly" as the BBC unveils his first full-length episode of Doctor Who.

"I was keen he be a little darker," he told the BBC's Lizo Mzimba. "He's struggling with himself and who he is."

The 56-year-old, who played abrasive spin doctor Malcolm Tucker in The Thick of It, is one of the oldest actors to have played the TV time-traveller.

Yet the Scot joked that, if anything, he was too young to play the role.

I think the whole spoiler thing has taken over the media Peter Capaldi

"I don't feel elderly at all, and I don't think the Doctor's elderly, apart from the fact he's two-and-a-half thousand years old.

"There's a magic about him which is not about being in your 20s and 30s," continued the actor, whose immediate predecessors - David Tennant and Matt Smith - were 34 and 27 when they first appeared in the show.

"We don't consider the Wizard of Oz or Father Christmas to be too old. They're still magical characters, and the fact they've been around the block only adds to their magic."

Deep Breath, the first episode of the new series, had its premiere screening in Cardiff earlier and had a second airing at the BFI Southbank in London on Thursday night.

The programme, which also features Jenna Coleman as the Doctor's companion Clara Oswald, will be broadcast on BBC One on 23 August.

After the London screening, Capaldi described his Doctor as "funny, joyful, passionate, emphatic and fearless."

"The Doctor is closer to me than Malcolm Tucker was," he said.

He also revealed he had met ex-Doctors Smith and Tennant to discuss the role.

Deep Breath - a spoiler-free first look

By Tim Masters, BBC arts and entertainment correspondent

As previous post-regeneration stories have shown, the Doctor can be erratic, wild-eyed, get his names mixed up and spend a fair amount of time in bed.

Capaldi gets to do all this in Deep Breath - and from the moment he first steps out of the Tardis in Victorian London with a dinosaur on the loose, there's little doubt he's a perfect fit for the role.

With its 80-minute running time, this episode gives Capaldi's Doctor plenty of time to explore his new identity. The frantic pacing of some of the Matt Smith era seems a thing of the past.

Writer Steven Moffat uses dialogue-driven scenes to explore this older-looking Time Lord. There is talk of his lined face, grey hair and eyebrows ("You could take bottle tops off with those.")

The issue of the Scottish accent, too, is brought up: there are a couple of good jokes about it, and then the story moves on

This is as much about Clara (Jenna Coleman) as it is about the new Doctor. His companion is clearly out of her comfort zone as she struggles to cope with this stranger who is now at the Tardis controls.

Hardcore fans will pick up on some references that hark back to the classic era, but the main thrust is one of looking forward.

The Doctor may look older, but the show - which celebrated its 50th anniversary last year - seems rejuvenated.

'True to your instincts'

Image copyright Getty Images Image caption Capaldi with Jenna Coleman outside Cardiff Castle on Thursday, for the series premiere

Concerns were raised earlier this year when five of the series' scripts and unfinished scenes from six episodes were inadvertently made accessible online.

Yet Capaldi - previously seen in a 2008 episode of the show with Tennant's Doctor - said the leak was "just one of those things" and "not the end of the world".

The show, he went on, "only lives in the finished cut" with all its production values, music and special effects completed.

"I felt sorry for everyone who'd worked on the show but the fans have been incredibly supportive," he said.

"Is it really so important? I think the whole spoiler thing has taken over the media."

The first screenings of the new episode coincided with the release of a letter signed by 200 public figures urging Scotland to vote "No" in the upcoming independence referendum.

Yet the Glasgow-born actor refused to be drawn on where he stood in the issue.

Talking about taking on the role, he said: "There's nothing I can do except do my best. Not everyone's going to like me, but that's life.

"It's such an iconic character and you don't want to let people down. At the same time, you have to be true to your own instincts as a performer and an artist."

Image caption Jenna Coleman's character Clara Oswald (left) was also the 11th Doctor's companion

Image caption Madame Vastra, played by Neve McIntosh, returns in the eighth series

The director of Deep Breath is Ben Wheatley, the British film-maker behind such cult titles as Kill List, Sightseers and A Field in England.

Keeley Hawes, Michelle Gomez and British singer Foxes are among the guest stars lined up for the new series.