Be afraid: The Daleks congregate. Credit:BBC To launch this new iteration of Doctor Who the series returned to its most bankable guest monsters: the Daleks. But the story which launched Troughton's tenure, The Power of the Daleks, was junked in a cull of the BBC archive in the late 1960s and has not been seen since. Until now. Previously junked Doctor Who stories, such as The Web of Fear and The Tomb of the Cybermen, have surfaced as 16mm film prints, the format used in the 1960s and 1970s for international program sales. In fact The Power of the Daleks was sold only to three countries: Australia, which returned the film print (after which it was destroyed), and New Zealand, who sent their copy to the third buyer, Singapore. The whereabouts of that 16mm print remains unknown. With little chance of the surviving print surfacing, the BBC instead commissioned an animation of the episode which has been married to a remastered fan-recorded audio track. The producer and director of the project, Charles Norton, described it as "the most ambitious Doctor Who archive restoration ever attempted". For Wills, now 75 years old, it represents a chance to look once again at a serial she filmed five decades ago. "They've taken that very small piece of tape that a teenage boy had laid on his tummy, and recorded off his television, and then they have expanded that now into wraparound, stereophonic sound," Wills says. "It's extraordinary."

The Doctor has always dressed with natty style. Credit:BBC The Power of the Daleks is significant in Doctor Who fandom for a number of reasons, notably that it was not written by Terry Nation, the creator of the Dalek monsters and the author of most of their early television appearances. Nation tended to repeat himself thematically, so The Power of the Daleks represented a departure, into darker, more complex storytelling. Here the Daleks are initially seen as technological relics, exhumed from a crashed space ship in a "mercury swamp" on the distant Earth colony of Vulcan. When revived they become servile machines but, as the Doctor suspects, are merely biding their time, scheming in the shadows, before taking over the colony and exterminating its inhabitants. Fear is the natural response to the Daleks – unless you are Doctor Who. Credit:BBC "David Whitaker, brilliant writer, and of course, when in doubt [in Doctor Who] bring back the Daleks," says Wills. "They threw everything that they could at it, because they wanted the show to go on. For us, we thought it was a very good script and when you see the animation, oh boy, oh boy, and the sound is astounding."

On the big screen in black and white – a colour release is coming in the new year – Wills says the story's tension is lifted to new heights. "Those old Daleks, they're absolutely terrifying all over again, and we have the wonderful scientist, Lesterson, who is going palpably mad," she says. "A brilliant cast, a great director, a new Doctor, you know there was no doubt actually that it was going to work." Of Troughton himself, Wills has nothing but affection. "How long have you got?" she says, reflecting for a moment on one of the most-beloved Doctor(s) Who. "The man was mesmerising, he was the most sweet, humble, ego-less person you could possibly wish to meet, and, of course, one of our most brilliant actors," she says. "He was an astounding actor, but he also was a very, very sweet person and with tremendous humour and intelligence," Wills adds. "All that, he brought to the part, and if it hadn't been him, we wouldn't be talking about Doctor Who today, because he definitely, absolutely and without a doubt, rescued the show." As for Doctor Who itself, the commercial success of The Power of the Daleks – it has been screened in cinemas in the UK, the US and Australia and will be released on iTunes and on DVD – may prompt the BBC to give other "lost episodes" a similar treatment. Presently – and including the six half-hour episodes of The Power of the Daleks which are still, technically, missing – 97 episodes from the first six years of Doctor Who are still unaccounted for and they leave a total of 26 multi-episode serials from the eras of the "first" and "second" Doctor incomplete.

Some are arguably forgettable. Others, such as The Daleks' Master Plan, The Tenth Planet, The Moonbase, The Evil of the Daleks and The Wheel in Space remain classics within the show's canon. For fans, a suite of animated reboots would be most welcome. For Wills, they are time capsules – literally and metaphorically. "That was just the beginning of this wonderful adventure," she says. "How could I believe that I'd be talking onstage at the British Film Institute at the same moment it had been broadcast 50 years ago. Well, that's the world of Doctor Who, it continues to surprise me with its magic." WHAT The Power of the Daleks WHEN ABC iView, from Monday, December 26