Is it a rock doc, a musical, or something else entirely? Two of The Lost Disc's creators tell Si Hawkins why they're tempted to keep it a secret.

"This isn't a workable model for other people to follow," admits Will Adamsdale, as he reclines in an easy chair next to some hefty motorcycles, slightly uneasily. "It's taken forever."

It's a Thursday lunchtime in East London and I'm in a biker joint with Adamsdale - the award-winning writer/actor/comedian - and his current director and co-writer Tom Parry, which sounds a weird clash of people and place. But this particular hog hang-out, The Bike Café, is next door to one of their regular onstage haunts, Shoreditch Town Hall. Imagine if someone remade From Dusk Til Dawn in the arty bit of East London, this is where they'd all end up.

Drinks lined up (ok - latte, coffee, herbal tea) we get down to some serious chat, about the quality of fabric in Bruce Springsteen's tour t-shirts, technically bad but actually brilliant rock singers - and eventually, comedy, which they're best known for. The erudite Adamsdale won Edinburgh's Perrier Award in 2004 for his character show Jackson's Way, and has been making ingeniously hard-to-categorise shows ever since. And the more effusive Parry is one third of the mighty sketch troupe Pappy's, but is increasingly in demand these days as a director.

They're here to talk about a show they've created with another mixed-up talent - the acclaimed writer, actor and jazz musician Ed Gaughan - and which, in some ways, they don't actually want to talk about, too much. The Lost Disc is a comedic music odyssey born out of a pet project that Will and Ed had spent years tinkering with. Then Parry got on board and pushed them "out of our comfort zone," says Adamsdale, "which is basically total obscurity."

Indeed, and they are now ready to unveil the finished show, with a first full run at the Soho Theatre beginning on October 8th, in the suitably evocative downstairs cabaret bar ("they should lift the smoking ban for this show," says Will).

What is The Lost Disc? Well, it's partly a gig - with live music from cult band The London Snorkelling Team, co-written by Fringe First winner Chris Branch - but with an intriguing narrative: the tale of a disgraced music journalist searching for three semi-mythical singers, and that titular record.

Some of the people mentioned in it are real, some are characters with such huge backstories they might as well be real, and the whole thing sounds absolutely made for those of us obsessed by comedy, music and mysteriously elaborate theatrical projects. The question is, what are Will and Tom willing to reveal?

How did The Lost Disc come about?

Will: I had these ideas for characters. A friend and I are obsessed with ['60s folk legend] Donovan, his seductive pretentiousness. He's kind of great, but half the time you're thinking 'what are you talking about?' So Roger LeFevre came out of that - we actually pitched him as a radio thing, but for some reason they didn't want to do stuff about music at that time, which was quite interesting. So we shelved it.

Then there's this other musician, a crooner, one of those guys on jazz documentaries who talks about the phrasing, how he fits too many syllables into the lines but he's really proud of it. And he sings Christmas songs all year round. We'd been working them up at these comedy nights at Shoreditch Town Hall, a sprawling version of both of these guys. But we needed a third one - and we realised we needed some direction.

Tom, what's your connection to Will and Ed?

Tom: Ed had directed Pappy's Last Show Ever, and we'd stayed in touch. He came to me and said 'we've got this Lost Disc thing.' 'What is it?' 'God knows.'

Will: I'm quite intrigued by that meeting.

Tom: He said "there's these two singers, but we want there to be three of them, and there's a conspiracy involved." At the time there were all kinds of things - the assassination of JFK was mentioned, the communists were involved, it was this sprawling two-and-a-half-hour thing. But the one thing that was entrenched were the characters and the music - 'we have to work with these guys and these songs.'

What I like, the story of The Lost Disc, it's very much the same as the process. You watch the show, you go through the journey with this journalist, and by the end you're sucked into this mystery with him. And it's exactly the same as working with Will and Ed, because by the time I came on board, it was me looking at these two weirdos hunched over this thing, then you're in there with them and you disappear down this rabbit hole.

Will: I've got a photo of Tom stood next to this whiteboard, with a crazy diagram of arrows pointing towards Mossad, Kennedy, 'Was Sinatra Involved?' A lot of that went on. We did a lot of writing to hammer stuff out.

Tom: And the music, it's not taking the piss, the sound is so authentically created, it's from a place of love and understanding.

You can get away with some weird and wonderful stuff in between, if the music's good...

Tom: It's so true. One of the things I love about musicals - you can punch through an audience's cerebral frontal lobe, where they're thinking about stuff, and just make them feel. It's a lovely tool to have and I think we use it in a nice way. You get them here [grabs heart]. That's what music does - make them feel first and think later.

The first 15 minutes of this show, you're thinking 'what is this I'm watching?' but by the time the first song kicks in - which is a banger - the audience realise they have to take us seriously. 'Fucking hell, listen to that!'

We did it at Latitude, and you could see people going 'what is this?' then the music starts and 'woah!' I was watching people walking past then coming in because of the band. It earns you a respect from the audience.

I can imagine it being quite intriguing at Latitude, as it's a music festival too, people not knowing what's real and what isn't.

Tom: It really was. The narrator gets up and says "I'm Stu Morecambe, former 6Music DJ." And at Latitude, at 10.30 in the morning in a marquee - absolutely, he could be. You could see people going 'is he?'

So The Lost Disc is sort of his show-within-a-show, as he looks for this record?

Tom: You spend three episodes with the singers, then we weave together how these characters could have possibly ended up recording together. The person who's investigating that is Stu Morecambe, the disgraced music journalist. This lost disc has become his life's work.

What I love about this show, from an outsider's point of view, it absolutely reflects the process. I'd just come off the back of six months working on this TV show - a soul crushing experience. Then coming into this show, and these two guys who are obsessed with these musical characters, and those characters are all obsessives. It's a show that has no real commercial goal. The reason they're doing it is because they love it. It was the perfect project to come into, for me.

Will: There are too many people in it as well. We were thinking of taking it to Edinburgh, but there's the cast, and a band - but that's what makes it fun.

Tom: Ed is a proper jazz guitarist, and his process is intrinsically linked with jazz, you can see it - trying to pin Ed down to a script is impossible. And long may that last.

You're clearly all big music fans - it sounds very immersed in reality.

Tom: Ed was on a train down from Sheffield and Jarvis Cocker was on it, so Ed said "we're making a show and you're in it, do you want to come and see it?" So they were chatting for 20 minutes. The relationship between reality and fiction in the show is paper thin, and that's how we want it, it dances between them.

Will: There are a lot of real people in there. Roger's more real than not in some ways.

Tom: Will and Ed have been living with these characters so long now - the show is an hour fifteen, but the world of it is so much bigger. The Lost Disc universe is huge.

Will: Stu imagines it as a 20-part Arena special, but he's had to curtail it.

Tom: We're also doing these afterparties at the weekend shows, where we get to do the songs in full, and some covers. Because the songs are so much fun to play, and the band never get the chance to fully cut loose. But even that's opened up this can of worms - 'what songs and covers shall we do?'

Will: We'll take the Soho basement to three separate decades. Actually, at Shoreditch Town Hall it was in the pit: the basement. We did it at the Vaults [in South London]... we'll only perform underground!

It's an underground musical. But presumably it's a lot more accessible with Tom on board?

Will: He's been good for us, and I'm really excited to be putting it somewhere where people might actually come and see it. But at the same time you don't want it to be 'ta da!'

Tom: Will usually takes two or three years to put something together, to have the idea and let it gestate. Whereas I said "we're doing this in six weeks."

Will: It was like a heist.

It sounds like a show that could bring a whole different audience in: your own fans, but also the music heads...

Tom: Yeah. I think we've made a show that we would love.

Will: And you'd love it even more if you found it by mistake.

The Lost Disc is at the Soho Theatre from Monday 8th to Saturday 27th October. For tickets visit sohotheatre.com