For nearly as long as Big Finish had been producing Doctor Who audio dramas, fans of the series had begged the production team to adapt a range of unmade scripts from the original TV series. Exotically titled stories like The Nightmare Fair, Mission to Magnus and The Foe from the Future had been endlessly discussed in fanzines and on forums, tantalising the series' followers with could-have-been adventures.

But it wasn't until 2007 when Big Finish line producer David Richardson joined the company that the idea of full-cast adaptations were seriously considered. A lifelong fan of Doctor Who, David well remembered the series' infamous 1985 hiatus, which led to the cancellation of many in-development scripts.

'I remember the bitter disappointment,' recalled David, 'particularly as we'd already heard that the new series would have featured the return of the Celestial Toymaker, Sil and the Ice Warriors. When the show returned but without The Nightmare Fair and Mission to Magnus, it felt like we'd lost a bit of Doctor Who history. Of course, these stories were later novelised, but even so I'd always wanted to see them realized as productions with the original actors. So when I joined Big Finish in 2007 I proposed the idea of doing the missing stories on audio.'

The recent success of the Doctor Who Stageplay adaptations convinced Executive Producers Jason Haigh-Ellery and Nicholas Briggs to commission the series, which would all feature Colin Baker as the Sixth Doctor and Nicola Bryant as Peri.

David quickly managed to secure the rights to Graham William's Doctor Who: The Nightmare Fair – featuring the return of the Celestial Toymaker (david bailie) - and Phillip Martin's Doctor Who: Mission to Magnus, which included the return of both the Ice Warriors (Nicholas Briggs) and the scheming Sil (Nabil Shaban).

'It did seem like a really momentous endeavour,' said David, 'Here we were, over two decades later; making stories that the late John Nathan-Turner had hoped to produce in the 1980s. The young David Richardson would have been screaming with excitement had he known back then!'

Production was off to a great start - but complications arose when plans to use two of the most-demanded stories – The Ultimate Evil and Yellow Fever and How to Cure It – fell through. To fill the gap, David extended his research to stories from outside the cancelled Season 23; and uncovered some hidden gems which fans hadn't even heard rumours of.

Doctor Who: Leviathan was submitted to the Doctor Who production office in the mid-1980s by Brian Finch: the creator of beloved science-fiction series The Tomorrow People. Brian's son Paul Finch read about the plans for the Lost Stories in Doctor Who Magazine and contacted David about the still existing script. David was delighted, and commissioned Paul to adapt the story for audio.

'Leviathan was a personal favourite of mine from Series One, and also a hit with Doctor Who fans.' enthused David. 'Which is interesting, because no one knew anything about the story before the scripts landed on my desk – I must confess, at first I thought it was a hoax... until I read the authentic pages from the 1980s. Paul Finch told me how his father had dreamed of getting a Doctor Who story made. I was so pleased that his wish had finally been fulfilled, albeit sadly after his death'.

The popularity of Leviathan later led to Paul receiving a commission to write a prequel to the story. Doctor Who – The Companion Chronicles: Sentinels of the New Dawn was released in April 2011, starring Caroline John.

The Lost Stories Series 1 continued with Christopher H. Bidmead's Doctor Who: The Hollows of Time. The story saw the return of classic series monsters the Tractators, and pitted the Doctor against the enigmatic Professor Stream (David Garfield). The character was originally written to be revealed as Time Lord villain the Master; until the BBC asked Big Finish to avoid using the character, due to his appearance in the television story The End of Time. Stream's identity is thus left up to the listener to decide...

Doctor Who: Paradise 5 was devised by well known scriptwriter PJ Hammond, who had created the classic fantasy series Sapphire & Steel. Hammond's script was originally written for inclusion in The Trial of the Timelord series and contained many elements from that season long story arc. Andy Lane adapted the script for audio, creating an entirely new opening episode to put the events in context. Hammond was pleased with Andy's new additions, and wrote him a long letter of thanks.

'Peter was just the single nicest man on the planet,' remembers David. 'Enthusiastic, endlessly helpful and generous, he made the whole production feel like something special and it's no surprise that Paradise 5 has gone on to become one of the most popular of the Lost Stories. I think it's superb.'

The range's sixth story was Doctor Who: Point of Entry by Barbara Clegg, who had written the classic series story Enlightenment. Barbara wasn't available to work on the audio adaptation, so David chose Marc Platt to continue her work (Marc having contributed to the original series himself with 1989's Ghost Light). An early effects edit of the story proved to be too gruesome for David, who asked for the gory sounds to be made more sci-fi – in keeping with presenting these stories as close to the version that would have been on television as possible.

Doctor Who: The Song of Megaptera by Pat Mills perhaps had the most complicated road to production, having been submitted as a story for the Fourth, Fifth and Sixth Doctors.

'This one would never get made! It's cursed!' explained David. 'Or so they told me... but actually Song of the Space Whale was pretty easy going on audio. Pat wrote the script, it was excellent. He did minor rewrites and then we made it. All very happy and jolly, and with none of the angst that had surrounded this on-off production for 30 years.'

But even once recorded the story still faced a final hurdle, when a similar Space Whale was due to appear in the Eleventh Doctor story The Beast Below; leading to a final name change to The Song of Megaptera.

The final story in Series 1 was Ingrid Pitt and Tony Rudlin's Doctor Who: The Macros. Ingrid, a well known star of classic horror films, was asked to write the story with her husband Tony while filming the Fifth Doctor story Warriors of the Deep. Soon after being commissioned by Big Finish, Tony's computer suffered a catastrophic hard drive failure, leading to the writers recreating the entire story from memory! A special scene between the Doctor and Peri reflecting on how their relationship had changed across the eight adventures was written by David for inclusion in the story.

The positive reaction from listeners to the first series of adventures led to the quick commissioning of two further box-sets of stories, this time taken from the Sixties era of the series. Doctor Who: The First Doctor Box-Set adapted two stories by Moris Farhi, both starring Carole Ann Ford and William Russell. Unlike the earlier Lost Stories, this release would be presented as a dramatised reading, similar in execution to Big Finish's Doctor Who Companion Chronicles. Doctor Who: Farewell, Great Macedon depicts the First Doctor, Susan, Ian and Barbara's visit to the court of Alexander the Great, performed by regular Big Finish contributor John Dorney. The script was adapted by Nigel Robinson.

'I was absolutely delighted, and thought it was an enormous privilege,' recalled Nigel on being asked to contribute. 'Hartnell is my favourite Doctor and I've always been a great fan of historicals. Funnily enough, one of my favourite characters in history is Alexander the Great, so everything just seemed to fit together... John Dorney does an absolutely wonderful job portraying him.'

Nigel also adapted the second story for the box-set. Doctor Who: The Fragile Yellow Arc of Fragrance was originally written by Farhi as a test piece for working on the series. In this unusual story, the travellers have been enjoying an extended holiday on the utopian planet of Fragrance; before their presence begins to lead to disaster for the planet's inhabitants.

The subsequent release Doctor Who: The Second Doctor Box-Set presented two very different types of stories. Dick Sharples' script for Doctor Who: Prison in Space was adapted by Simon Guerrier, starring Frazer Hines and Wendy Padbury. An authentically Sixties comedy tale of a female-dominated planet, the full-script for the unmade production was put into production when it was uncovered in Frazer Hines' garage!

The set's second story didn't feature the Doctor at all; and was in fact a pilot for the very first Doctor Who spin-off series. The Daleks: The Destroyers was devised by Dalek creator Terry Nation to sell to US markets and featured the return of Sara Kingdom (Jean Marsh) and her fellow Space Security Service agents (who had first appeared in Mission to the Unknown, before aiding the Doctor in the epic story The Daleks' Master Plan). The episode was adapted by both Nicholas Briggs and John Dorney, while Jamie Robertson created an authentically Sixties theme for the series.

The two box-sets added to the already diverse line-up of the Lost Stories. But there was still a lost era ripe for exploration; the unmade 1990 series starring the Seventh Doctor (Sylvester McCoy) and Ace (Sophie Aldred). Former television series script editor Andrew Cartmel was invited to bring his unmade stories to life.

'I was just delighted, really,' said Andrew. 'It felt very strange, as you can imagine, because the series never happened, and I'd got into a frame of mind where I didn't think it ever was going to happen... there were no scripts as such... most of what we had was in our heads. I spoke to Ben Aaranovitch and Marc Platt about what we had, and they remembered a surprising amount, especially about the one we're calling Crime of the Century.'

Doctor Who: Crime of the Century introduced new companion Raine Creevy (Beth Chalmers) to the series – an aristocratic safecracker whose appearance had long been anticipated by fans after decades of articles exploring the unmade episodes. Raine's story ties the four releases together, being born in Marc Platt's opening instalment Doctor Who: Thin Ice.

'She's smart, she's sassy, and she's got a wonderful rapport with the Doctor,' said David on Raine, 'The dialogue sparkles between the pair of them. Everything that was planned is there, like her family history and her relationship with her father... Andrew has realised that beautifully.'

The series also delivered on many much wanted scenes that had passed into fan-legend, including Ice Warriors in Sixties London (Doctor Who: Thin Ice), the Doctor meeting Raine by hiding in a safe (Doctor Who: Crime of the Century), the return of Brigadier Bambara (Angela Bruce) and UNIT in Doctor Who: Animal and Ace as the Captain of a starship in Ben Aaronvitch's Doctor Who: Earth Aid.

David was pleased with the four stories, particularly with being able to finally bring Raine to life.

'She was brilliant, wasn’t she? I love Beth – she’s just the most accomplished actress, and just the nicest, funniest person to spend time with. It’s been great to take her to conventions, and see her get the attention from fans she deserves.'

The Lost Stories had already succeeded in bringing to life four eras of classic unmade stories. But the range was really just beginning; and the recruitment of Tom Baker to Big Finish was about to open up a whole new decade of Lost Stories...

Join us tomorrow for Part 2 of our complete guide to Doctor Who: The Lost Stories. You can order the entire run this weekend at special offers prices, with series bundles also available. Click here for more details.