The classic sci-fi series Timeslip is revived by Big Finish as original series lands on BritBox

Airing a total of 26 episodes, broken up into four interlinked stories, the show earned a strong critical reception in the early '70s and has won a cult following for tackling themes like cloning and climate change, and for its exploration of complex themes including man's reckless pursuit of scientific advancement and abuse of technology.

"Without doubt, its enduring success and strength was the fact it was character-led and it was story-led," star Banks tells RadioTimes.com, 50 years on from Timeslip's original broadcast.

"It resisted going into the area of fantasy science-fiction – monsters, galaxies far, far away... all of which have their place, but fans always talk about the relationship between Liz and Simon, and the story. The fact that it was a 26-episode continuing arc was quite unusual for those days... and I think that's what captured people's imaginations."

"It’s not written down [to the audience], it’s actually quite adult," agrees Marc Platt, a writer on the classic Doctor Who series who has also penned one of Big Finish's new Timeslip outings.

"It’s just so intriguing and has this potential because they keep jumping to alternative versions of the same place. It’s journeys in time not space."

"There’s a tone to it that sets it apart," adds fellow Big Finish writer John Dorney. "If you look at something like The Tomorrow People [also produced for ITV in the early '70s], it feels a bit more for kids than Timeslip ever did. Timeslip at times requires quite a bit of actual energy I think, from the viewer. Which is particularly interesting from a children’s programme, but then I think TV was different then, so they could afford to take their time."

"Slow isn’t bad," Dorney continues. "It gives you detail, it gives you a certain richness and scale and I think Timeslip is the definition of measured. It is a really rich and complex piece."

Though a sequel to the original series was mooted, it never materialised for a variety of reasons – the first 26 episodes had gone significantly over budget, with a failure to sell the series overseas also playing a part, while series producer John Cooper also felt that Timeslip had run its course.

"There was discussion [about a follow-up] as it finished," Banks recalls. "But after a relatively short period of time, I remember having a phone call from John Cooper who, as gently as possible, said that after various discussions, it had been decided that they wouldn't be carrying us forward.

"I was hugely disappointed, but I remember, in his incredibly quiet and well-mannered way, he said, 'I know it's disappointing, but perhaps it's the right decision' – and looking back now, with hindsight, I think it was probably right. It's that fond memory of those 26 episodes that's remained with people, which is terrific."

In the 50 years since Timeslip premiered, its leads Banks and Burfield have remained "the best and closest of friends, lifelong friends" – Banks was an usher at Burfield's wedding, while she's godmother to his eldest daughter and Burfield's husband was best man at Banks' wedding.

But even so, Banks says it feels "a little bit surreal" to be revisiting Timeslip five decades on, as the show becomes the latest piece of cult programming to be revisited and revived by Big Finish as an audio series.

"The opportunity to revisit something that you worked on 50 years ago is quite unusual, and very exciting," says Banks. "I can't believe it's quite happening," echoes Burfield. "I mean, who'd have thought, 50 years later, we'd be playing the same characters?"

The new Timeslip reflects the passage of time in our world, being set decades after Liz and Simon's childhood adventures and sees the now-adult pair encounter two youths from the 1980s, Neil (Orlando Gibbs) and Jade (Amanda Shodeko), and realise that the barrier is open again.

"It's remained true to the concepts of the original," Banks says of the revival. "I think the tone [of the original] is very similar in the stories that we’re telling, they are very much of an ilk," echoes writer Dorney. "Though there’s a degree to which you don’t write things in a vacuum, so it’s going to be influenced by modern storytelling techniques."

Big Finish's take on Timeslip - which spans two adventures, this month's The Age of the Death Lottery and June's The War That Never Was – will, like the original, explore topical themes through a fantasy lens, including overpopulation.

The sometimes terse but ultimately affectionate relationship between Liz and Simon is another constant. "We could see the characters that we played in these [new] scripts, which can't be easy to do," says Burfield.

"The first interchange between Liz and Simon is quite a curt exchange over the phone, so that clash is still there, but it does warm as the story progresses," says Banks. "As it did during the original," adds Burfield. "One minute they're at each other's throats, the next minute they're trying to save each other... it's still thus!"

Timeslip Volume 01: The Age of the Death Lottery is available now from Big Finish. Volume 02: The War That Never Was will follow in June. The original Timeslip episodes 1-6 are streaming now on BritBox.