After three series and four years as the Doctor, Peter Capaldi is soon to film his last episode of Doctor Who. For a lifelong fan of the show, leaving can't be easy and yet the actor says his decision is based on his determination to only give his best to the part.

"I love this show, but I've never done anything where you turn up every day for ten months," says Capaldi in the new issue of Radio Times magazine. "I want to always be giving it my best and I don't think if I stayed on I'd be able to do that. I can't think of another way to say, 'This could be the end of civilisation as we know it.'"

Capaldi adds that the cyclical structure of Doctor Who means that it is not necessarily something that an actor seeking new challenges would want to work on indefinitely. 

"With episodic television of any genre, the audience wants the same thing all the time," he says. "But the instinct that leads the actor is not about being in a groove."

Read the full interview with Peter Capaldi – as well as his co-star Michelle Gomez and Doctor Who showrunner Steven Moffat – in the new issue of Radio Times magazine, on sale from Tuesday in shops and via iTunes