Two softly-spoken family men settle down in a plush London hotel to explain the thinking behind their latest comic creation. The fact that it involves an embittered, one-handed children's entertainer; a telekinetic dwarf in love with Snow White; a blind avaricious collector; a midwife who treats one of her practice dolls as a surrogate child; and a serial-killer-obsessed man-child, provides an immediate clue that the pair are Reece Shearsmith and Steve Pemberton.

The five disparate characters in Psychoville, their new murder-mystery comedy for BBC Two, are linked by receipt of letters saying, "I know what you did." Drawing on a similar style and imagination to their previous work, while being distinctive in its own right, Psychoville also in part reflects their lives as fathers of young children. Fatherhood certainly hasn't softened their creative style or dampened their magpie-like ability to take intriguing human traits and assemble them into disturbing but recognisable characters, if anything it's become a new source of inspiration. "Having young children, we're in a constant round of parties and the children's entertainer is something pertaining to our real lives" says Reece. "The midwife has also become big - that strange thing where dolls are dished out and you have to hold them comes from that shared experience - the horrible nature of the dolls has stuck with us."

So what exactly is Psychoville and how did it come about?

Steve: We sat down over two years ago and Reece and I decided to write a new project; we didn't know what it was going to be or what format it would be in, we talked about doing a sitcom or a traditional sketch show. But one of the ideas that really stuck with us was the idea of doing some kind of mystery or thriller, a comedy but with a different sort of genre aspect to it as well, so the idea of doing a comedy thriller really appealed.

Reece: It kind of was born out of that love of 24, Lost, Heroes and Dexter, those things that kind of hook you in with a cliffhanger every week. We thought that it could be done with a comedy, though it's a very different set of people that watch those things. We thought if it was intriguing enough and had our sensibility, it would be a great thing to marry those two worlds.

Steve: It's very difficult as well, because all those examples are of course American series, they get 20-odd episodes to develop characters and storylines and we get seven but we've packed 22 episodes worth of plot into seven half-hours and some jokes as well. Basically, Psychoville is a dark comedy thriller.

How did the idea come about?

Steve: We had shows in the back of our minds that were thriller shows where you followed a narrative and if you missed one episode you really felt like you had to catch up and seek that episode out. That's what we hope people will do with Psychoville. If you happened to miss an episode, then you will feel bereft because it's a driving narrative. What was really tough was blending those elements of a successful comedy show which delivered the same characters every week, familiar jokes but also giving a really exciting narrative. It was a very organic process and that's the way we wanted to do it. We wrote one episode and then we had maybe three or four month periods before the next one was commissioned. And then we wrote the second episode. We got halfway through writing the series and we raised a series of questions.

Reece: The same way we used to do with The League Of Gentlemen, there were certainly homages to things, nothing is parodied. If we're doing a horror bit, we fully go for the horror, or a thriller. In hindsight it occurred to us that a lot of inspiration was very Hitchcockian, and that's because of the way it panned out being this thriller element to it. It was great writing it, but not quite knowing where we were going with the plot because it means you can't possibly work it out. So it was a challenge as there was an element of ourselves having to untangle the riddle, it's more surprising because we were stuck ourselves at points. We love all the films or programmes that genuinely surprise you. I hope we've managed it. All the characters have got their own stories, but they've got this mystery that's catching up with them and that all resolves itself at the end - well nearly, not quite, we've left the door open for more perhaps.

Do you worry about taking things too far?

Reece: Again, it's the wrong way round to say 'what can we think of that's going to horrify someone'. When it happens it happens, it almost surprises us that we've arrived at something odd or strange - you don't have something in mind and try to shoe-horn it in. The story takes you to the more extreme places; that's the right way round.

Steve: We want to surprise people - not because we've done something gross or whatever - I think we have an in-built sense of the right things to do. There are some disturbing, weird images in there, but audiences like to be challenged. It's the same tone as The League Of Gentlemen, it's called Psychoville, it's on late-ish... I think they know what they're going to get.

Tell us about episode 4, the episode that is shot virtually seamlessly in two long takes:

Reece: That was an accident that was never planned, because you'd never think to do it, it's a great episode. It became this big challenge that we set ourselves really. They asked us to do a seventh episode, "So it could just be you and Steve in a room," they said. We said "What do you mean? We've written this very elaborate interlocking story, you can't just slam in an EastEnders episode where Dot and Pat are in the launderette." But that's exactly what we did!

Steve: We talked about it, I was very dubious and said "What about (the Hitchcock film) Rope?" Let's have a look at it because we had this sort of Hitchcockian idea running through the series anyway so that was a great one to look at. It's set in one room, with the technology they had at the time they could do 10-minute takes, that's all they could do because the actual tape ran out. The cameras were as big as this room, it's not like today when you can strap a steadycam on, it was a huge technical achievement. There's something about not breaking the tension, it's like not blinking, you don't quite know why but something about it is unnerving. So we said let's try it. And because it's David and Maureen killing people, we'll start with them putting the body in a trunk, which is exactly how Rope begins. We came up with loads of ideas, loads of things that we weren't sure how to achieve without breaking the filming. But every effect in there, everything that happens, happens in real time.

We decided not to use a steadycam, it was too modern. We put the camera on a dolly. It was like a ballet that was going on between us the actors, two stage hands either side bringing on props, pushing furniture out of the way, the sound guy had the longest boom you've ever seen and would always be in the corner of the room. We actually shot some of it on DV camera showing how we actually achieved it because it's not something I've seen before because people do long episodes. Say in EastEnders it would be focusing on two characters, that's multiple camera and you've always got the choice to stop and re-take. We didn't, we kept going and it's something we're really proud of now. It does stand out from the other episodes, it's a special episode and hopefully people will really cherish it.

Tell us more about Psychoville online...

Reece: We knew from the word go that there would be a big web experience for the programme, that side of it allows you to explore the detail even more. The show is very detailed, so to give the characters a life outside of the programme on the internet was a great opportunity to add more jokes and a back story. So you can explore it for yourself. It was a challenge to make the experience a kind of puzzle for you to unlock in tandem with the programme. Quite an involved geeky thing to do but there are people that will do it. We're quite excited by the fact that it's hard to unlock and you've got to be quite vigilant to find the clues. It's all available on the web because after the episodes are gradually released, if you want to play the game, it's all there for you to kind of try and fathom from the start.

Steve: It's like SAW, if you work it out you'll find yourself locked in a room with everyone else who worked it out and one by one you'll be horribly killed (laughs). Online wasn't something we thought much about when we were doing The League Of Gentlemen. With the streaming video, uploading, creating forums and messageboards that we've seen during the time that The League Of Gentlemen's been on and then beyond, it's very much part of the way that the media's going. It keeps it alive. I think it's got to come from the people who do the show, we've written the bulk of the material for the actual website. We've worked very closely with the producers of the website to create a proper story so it's as detailed and as much a Psychoville experience as you're going to get, because we've actually come up with it. It's been really exciting to know that it gives the programme a whole new life.

Steve: Viewers can spot website addresses each week from which they can get a lot more info. There's also a question about one of the characters, asked by the person who's blackmailing them. We thought it was an exciting way of expanding it - we weren't asked to do it, we actually sat down and wrote it. Most people won't even notice but, for those who do, we want them to feel they are investing in a whole world. We hope people do bother, otherwise it's going to sink in cyberspace!

The pair also have central roles in two of the stories but, unlike The League Of Gentlemen, they don't play all the parts. Instead they've assembled an impressive cast. "We're in every show, but we don't dominate it," says Steve. "We've got people like Dawn French, Daisy Haggard, Eileen Atkins and Christopher Biggins playing himself. We worked hard to make the characters fun and interesting, so they'd say 'I'd love to do that'. Being actors ourselves, we know what's going to hook them in. There are whole scenes we're not in, which is very different for us. We ended up playing four characters each, two of whom are major and two quite minor. We love doing that, and it's what we're known for, but we didn't want it to become another League Of Gentlemen. We're very keen that this is its own show."

How do you know when you are onto something good, be it a character or a storyline?

Reece: It ends up being me and Steve sat in a room writing. If we both laugh at it you hang onto that moment. You can't just hope to write a catchphrase, you can't come at it that way round. You hope people will be intrigued by the characters, then you've got the back story and a little bit more information comes out. On a page looking at the line-up they are really extraordinary characters - you don't get those five in a room everyday. I hope they will stick in people's minds.

Can you tell us more about the characters...

Steve: The characters grew quite organically, in the same way the plots did. Having had several discussions about a format for the new show, we just said "Let's start writing, everything starts with characters". The fairytale element with Snow White seemed to be a theme because the Joy story has a Pinocchio feel to it, and then Jelly and his hook and Mr Lomax, they feel like quite classic situations. With episode one where you're setting up all these stories, it felt like it had a classic feel to it. They all felt rich enough to not just be the same joke played out seven times.

Steve: One of the first ideas we had, we were talking about our experiences of becoming parents and I remembered a midwife who did all the ante-natal classes and we started swapping notes and stories. Joy teaches ante-natal classes, she talks to prospective parents who are in very vulnerable positions in quite a cutting, nasty way about what they're about to go through. But her kind of secret is that she has one of her dolls that she uses in the demonstrations and treats it as if it's her real child. She absolutely believes that she can make Freddie into a real boy to compensate for something that's happened in her past. We also hit on this idea of treating Freddie as a real child. I do remember we had a Bristolian woman and she did say "And here he is, here's Freddie". And that was the starting point, as soon as we came up with the idea of the doll coming alive, it just added such depth to it.

Reece: We both recalled a doll, a very faceless, sackclothy horrible doll that dads get to hold, to experience what it's like to hold baby. Mr Jelly the children's entertainer was born out of me wanting to once again play an angry character, inappropriately in front of kids. I've played a lot of psychotic characters, many of them in the League and also in Vic and Bob's Catterick I played a particularly violent madman: I enjoy playing characters with a lot of built in rage! Mr Jelly is the latest in that particular canon.

Steve: It started off with Mr Jelly, he's a very scary children's entertainer. One of us suggested he had a hook, one of those scary attachments. But what really brought that to life was deciding there was a rival called Mr Jolly and that they were always getting confused. One was very good and one was very poor. So again, it was just that little twist on it that gave it life beyond being a sketch.

What about Mr Lomax, how did that character come about?

Steve: I remember writing in a notepad when we were doing The League Of Gentlemen, a scary old man that lives in a house and that if your ball went over the wall you'd be scared to go to the house to get it back, and some little child goes into the house and the man's holding the ball and he says "I knew you'd be the one". I like the idea of a serious-minded person with a very childlike obsession collecting 'commodities'. Once you put these two things together we were off. And the other thing was this great opening line which we'd had for a long time which Reece recalled somebody saying...

Reece: "Get your claw out of my holy of holies", which was a real line from someone's Dad I know. I was in his drawer and it was just full of protractors and books on the cosmos and he screamed that at me from across the room.

Steve: So we built that whole thing around "Get your claw out of my holy of holies". Also, I had a job reading to a blind man when I was a student, and so I knew it would be an interesting relationship between the man and his helper. I thought I was going to be reading a novel, but it was boring stuff like financial reports. Sometimes, he'd give me a text book and say 'go away and put that on tape for me'. I'd come to a graph and spend ages trying to describe it, until in the end I used to just turn the page and say "he'll never know!"

Maureen and David are interesting characters!

Reece: David's got an obsession with serial killers, which is not a million miles away from mine.

Steve: We had an idea, which was one of Reece's ideas for a long time to do something around Murder Mysteries and that's where that came from, because he's done a lot of those in real life.

Reece: Yes and it seems no-one's done it and it's a really interesting world. I used to do those murder mystery evenings where you pay £30 and some of the actors enact a murder. So we thought what if we put someone who's obsessed with killing in this world that's all very jolly, Twenties, very sedate Miss Marple type murders, very dignified poisonings. We thought what if he plunges in with a very modern Se7en / CSI type scenario and that would tip that world upside down.

Steve: Which is a bit like Theatre Of Blood, one of our all-time favourite films. You enjoy each week somebody being bumped off in quite an unusual way and you're almost with the killer, which is a bit like Dexter as well. It's not a whodunnit, you are seeing who's doing it and you know why they're doing it and you're almost by the end rooting for them.

Reece: There's a first image where she's testing him about Jack The Ripper, while scratching his eczema back. We didn't make that up. Someone told us they went to see a friend whose mother, an amputee, was scratching her son's back with her foot. We thought if we do it with the foot no-one will believe it, so we changed it. Even so, it's a startling image and something we would otherwise never have come up with.

Can you tell us more about Robert?

Steve: The character of Robert was a very strange birth, the small guy who's doing a pantomime, and he's in love with Snow White. We just came up with this idea of the sort of telekenesis, that sort of Carrie-like ability that he has to make things happen when he gets angry. To begin with it's out of his control but he learns to control it.

Reece: We like the parallel of Snow White And The Seven Dwarfs and him falling in love with Snow White and the fairytale element coming through in real life and the backstage of a theatre as well which is always great. It's a world you don't really see much of, but it would be fun to show the colourful panto itself and the mundaneness of the horrible dressing rooms.

Who is the black-gloved stranger?

Steve: The black-gloved stranger is seen throughout the series and you may or may not find out his or her identity until the very end. But it's really the thing that binds the whole series together. Each character has its own storyline and those storylines themselves are very involved and bizarre. But what is going over the whole thing and what is really the catalyst is what the black-gloved figure is trying to do - trying to punish these people for something they may or may not have done.

Reece: It's a revenge thriller really, the black-gloved figure has a vendetta against these people and it's how they execute that and gets them back to pay for their crime. With League we had the same idea really of not just wanting it to be disparate sketches. The story of the black-gloved figure and their past and the letters is the glue that binds this series together. They are all scattered around the country, and yet they have this unifying thing that gives you the outside story. The thing of this back story and what they've done is important. It's not just something to throw in every now and again to make them seem linked.

How do you feel about playing multiple roles again?

Reece: It was absolutely exhausting doing this kind of show where you do all the different characters. I got used to playing one part in other things. When you're an actor in someone else's thing it's easy, it's terrible to say it because other actors would disagree but you turn up do your lines and it's not your responsibility at the end of it. But of course if it's your thing, we've got half an eye on our "God we're overrunning" or "we're not going to get to that bit". It matters to us, it's our baby that we're trying to give birth to so to speak.

Steve: It was a conscious choice that we would play fewer characters, and whilst we did have a good array of characters, we didn't know exactly which characters we'd play right up until the last moment really. We knew they were all good strong characters, we knew we had hopefully the opportunity to get some good actors. So we chose two main characters each and a couple of subsidiary ones. I think the balance is about right, it is our show and we didn't want it to feel like we got lost in it but there's plenty more opportunities for people like Dawn French, Eileen Atkins, Daisy Haggard, Daniel Kaluuya, everyone we had was just fantastic and it became this great ensemble. When we did the read-through it was really exciting seeing all these faces around the table.

Inevitably some fans will wonder if Psychoville is the precursor to a full League Of Gentlemen reformation?

Steve: It's still a going concern, we've never broken up, but there was a decision to have a break, during which we wrote this. It has taken two years from writing the script to getting it actually made and on TV. There's no reason why we won't go back, we're still good friends, but to do anything together would need a year and getting everyone together is tricky.