Here has always been something profoundly cinematic about The League of Gentlemen. Although the famously off-kilter quartet learnt their trade in fringe theatres and the upstairs rooms of pubs - improvising scary porcine facial effects by sticking bits of Sellotape across their noses - their comedy was deeply rooted in celluloid from the outset.
They took their distinguished-sounding name from the title of a 1959 heist caper starring Jack Hawkins. The blasted psychic landscape of Royston Vasey, the compellingly claustrophobic Northern Gothic enclave which their army of dysfunctional characters calls home, clearly reflects the influence of classic British horror films such as The Wicker Man and Witchfinder General. And over the three series of their Bafta- and British Comedy Award-strewn BBC2 show, they have been widely praised for achieving Oscar-worthy production values on Children's Film Foundation budgets.
So now that they are finally stepping up a gear to make a feature film, the potential pitfalls are obvious. "We'll probably end up making it look like cheap TV," grimaces Mark Gatiss - arguably the most conventionally suave of the ensemble's four constituents - relaxing in a trailer whose mouldering beige upholstery bespeaks a wet weekend in Hastings more eloquently than a new life of Hollywood glamour.
We're at the production's base camp, in the latter stages of a frenetic six-week shoot. Despite the location - just off an unglamorous stretch of the Dublin ring road, next to a warehouse selling power tools - there is nothing downbeat about the atmosphere on set. In fact, in the latter stages of a frenetic six-week shoot, a nasty outbreak of flu has only served to intensify the can-do ambience.
"There's no reason why we can't make good, low-budget independent films in this country," insists the non-performing but fully operational League member Jeremy Dyson, evangelistically, in the back of a parked people carrier. "Films that are films - stories that can't be told any other way. We can do it. I know we can!" It's great to see the Gentlemen so enthused. There have been moments in the past few years when the unique esprit de corps which characterised their scabrous ascent into the UK comedy pantheon has threatened to dissipate in a welter of guest appearances in fair-to-middling TV dramas. But now a common cause - avoiding the artistic under-reach that has dogged so many of their comedic predecessors (from Morecambe and Wise to Kevin and Perry) in the leap from small to big screen - seems to have drawn the four of them back together.
"It would have been very easy to do a film where we all go to Majorca on holiday," admits Gatiss, "but we wanted to make something people would remember." The consequence is a "ludicrously ambitious" screenplay (working title League of Gentlemen: The Motion Picture), whose £4m budget will be stretched to its limits in the hope of encompassing three fully realised cinematic worlds, as well as "some dirty tuxedos, a pike battle with a stop-motion monster and a fiery climax with us running around like William Holden and Richard Chamberlain in The Towering Inferno".
Nothing too apocalyptic is underway as yet on this particular chilly Irish Thursday, though one of the rickety assemblages of ancient double-decker buses (without which no film or television unit base would be complete) is filled to bursting with extras, sumptuously attired in the costume of the late-17th-century court - a riot of perukes, brocade and beauty spots. The vaguely surreal effect is enhanced by the fact that they're on board eating an undeniably modern-looking lunch.
A few familiar faces stand out among the troughing throng. The first is The Divine Comedy's Neil Hannon, somehow looking more plausible as a 17th-century fop than he generally does in 21st-century clothes. Then, there's MTV film-show host Alex Zane, bidding to enhance his status as the Jonathan Ross of the text-messaging generation by spending a day as an extra, flaunting a photo of himself on the set of the sequel to Deuce Bigalow. The Faustian bargain which brought him here (we'll swap you a cameo for a nice bit of PR - free lunch thrown in) is only the beginning of the horse trading required to make a production on this scale happen. A flu-ridden Reece Shearsmith (whose alter-ego Geoff finds himself close to the centre of the film's events) admits that during the course of an 18-month wait for the final green light, a thought crossed his mind: "If we'd just done another TV series, it'd be on by now."
By the time the money came through from Film Four and Universal, their confidence presumably buoyed by the huge and not entirely expected success of Edgar Wright and Simon Pegg's Shaun Of The Dead, only a few last-minute compromises were necessary. Director Steve Bendelack - making an eagerly awaited feature debut, having brought us not only three series of The League, but one each of The Royle Family and Little Britain as well - will be shooting on new-fangled High Density Video rather than old-school 35mm ("If it's good enough for Collateral and Star Wars," says Gatiss, stoically, "it'll probably do for us"). A scene down a sewer has gone, apparently, but - glad news - "the whole Armageddon thing" is still in.
Producer Ed Guiney - a man well versed in the financier's smoke and mirrors of deferment and compatible tax breaks - is happy to supply a capsule storyline. "The writers have got sick of Royston Vasey," he explains, "but the characters need them to f continue with it in order to survive, so they track them down and discover that they're writing this other film - set in the 1690s - which they then invade." Well, that seems straightforward enough.
"We spent a couple of weeks flailing around at the start of the writing process," admits Dyson, "and the first thing that really made us laugh was an idea where Reece would come in as himself and say to Steve [Pemberton, the League's most instantly recognisable member, thanks to his role as Tubbs from the infamous Local Shop], 'I've just seen Pauline [malevolent Jobstart interviewer and long-time League favourite, also played by Pemberton] in Budgens.' We found this hysterical. At first we thought, we can't do this, can we? But then we thought, why not?
"If you're going to go down that road," he continues, waxing theoretical, "you can't do it from the writers' point of view. Not only is it not interesting, it just kind of makes you wince. But doing it from the characters' point of view felt quite original: we couldn't think of any obvious occasion where somebody had done that before."
The storyline - which Guiney describes, with infectious optimism, as "Charlie Kaufman meets the Marx Brothers" - certainly offers the actors opportunities to explore any mixed feelings about their characters, and encourages them to identify with those characters and against themselves. This is no bad thing - there were moments in the latter stages of The League's televisual odyssey when the need to keep themselves interested seemed to be driving them towards extremity for extremity's sake. Their feelings for their own creations at times seemed to have soured from something very like love to something uncomfortably close to hate.
"By the first episode of the third TV series," Dyson remembers brightly, "the characters were literally fucking each other. But in the film, Herr Lipp [Pemberton's innuendo-dogged German exchange teacher] gets to fuck a real woman who is a loving wife!" Well, not actually his loving wife, but to go into any more detail about the scene would diminish the impact of the most effectively creepy case of mistaken identity since Nicolas Cage and John Travolta in Face/Off. "So we're kind of looking outwards rather than inwards. It was quite fun turning ourselves into minor villains too," Dyson grins. "Although not me ... I'm very sympathetically portrayed."
Like a Hitchcock cameo in reverse, The League's non-performing member expresses his influence over the narrative by having himself played by an actor. If such meta-textual frolics recall the work of Hollywood wonderboys Spike Jonze and Charlie Kaufman, it's probably no coincidence.
While Pemberton is keen to point out that the team had their big idea before seeing Adaptation (in which Nicolas Cage's hard-pressed screenwriter finds the boundary between imagination and reality similarly porous), they'd already seen Jonze and Kaufman's previous film, Being John Malkovich, and thought, "Why can't anyone British do something this funny and clever, rather than making 'comedies' about bad rugby-league teams triumphing against the odds?"
Dyson is happy to admit that making good this transatlantic deficit is The League's highest aspiration, though he sounds a note of caution. "Of course, whether we pull it off or not remains to be seen. After all, the film's not finished yet ... "
Half a mile away, in a semi-derelict roofing warehouse, Shearsmith is poised above a long-drop toilet in a sumptuously oak-panelled royal chamber, with camera and sound crews clustered around him. A rather erudite gag about "popery" and "potpourri" leads swiftly into a gruesome episode featuring that most pitiable of historical figures "the night soil man", or "guardian of the royal stool".
This scene suggests that the more lavatorially inclined portion of The League of Gentlemen's fanbase (a fair percentage) won't leave this film disappointed. But Gatiss's willingness to describe the strange business of recording DVD extras at the same time as putting together the actual film - an activity in which he is busily engaged - in terms of both Marcel Proust and Heisenberg's Uncertainty Principle (once you've measured something, it changes) provides welcome reassurance that they have not closed their intellects down for the duration.
Among the few British film-makers who've managed a satisfactory union of scatology and metaphysics, the Monty Python team loom large. "They're the only people that ever pulled it off with any verve," says Dyson, of the jump from TV to cinema, with Jabberwocky and The Life Of Brian, "so they've got to be the model."
One of the guest stars hoping to help The League of Gentlemen emulate their illustrious example is the veteran British actor David Warner (whose credits include Terry Gilliam's Time Bandits, as well as The Omen). He points out an interesting contrast between the two ensembles. "When Monty Python do their sketches, they're very funny, but you know them as Eric Idle and John Cleese. With The League of Gentlemen, their creations have such depth you know them as the characters."
This has been both The League's blessing and its curse. "If you make a personality-driven show," Gatiss explains, with the feeling born of bitter experience, "you get a lot more attention and everyone wants to cast you in other things. If you try very hard to disappear into the work, people tend not to notice you."
Having sneaked a look at what appears to be an unusually polished (not to mention very funny) script, it seems The League have found a way of turning that very anonymity into a cinematic asset. Shaun Of The Dead's critical and box-office success on both sides of the Atlantic has shown what can be achieved by (in Gatiss's phrase) "giving people their head and encouraging them to make the film they want, rather than designing something generically British by committee". The omens could hardly be more propitious.
Later in the week, Simon Pegg and Phoenix Nights' Peter Kay will jet in to do their cameos (the former returning the favour for The League's blink-and-you'll-miss-them appearances in his own film) as Simon Pig and Peter Cow. Perhaps one day the new Britcom establishment will be constantly turning up in each other's films in the same way that Ben Stiller, Will Ferrell and the Wilson brothers do now in Hollywood ... it's a beautiful dream.
"I suppose we're a generation that thinks filmically," muses Dyson, pondering the divide between The League and their immediate comedic predecessors - Reeves and Mortimer, say, or Caroline Aherne, or The Fast Show's Paul Whitehouse - none of whom has yet made the break into movies. "It's there in our programmes - and in Simon Pegg's - where it isn't necessarily in, say, Vic and Bob's. Because they're 10 years older, I think they were inspired more by TV, whereas when we were growing up, our TV watching was completely mixed with our film watching, until the two blurred into one thing."
Perhaps one day, cultural historians will debate the impact of the generalised availability of video recorders on the changing aspirations of British comedy. For the moment, the location for today's big scene is finally ready. Another few hundred yards round the ring road, the Drimnagh Castle restoration project provides a sumptuously appointed balconied banqueting chamber for a grand court set piece. Victoria Wood's Mary is resplendent with a beauty spot and a giant wig, while Bernard Hill dissembles regally as her uncharismatic King William.
Downstairs in an improvised holding pen, the exquisitely costumed extras shiver around a single convection heater as they wait for their final call. Upstairs, Dyson and Gatiss gather excitedly around the monitor screen. They'd hoped the visual feast laid out before them might echo the Technicolor majesty of vintage films by the British director/writer partnership of Powell and Pressburger. It's a great pleasure to be able to say it does exactly that.
'League of Gentlemen: The Motion Picture' will be in cinemas next spring (though it may have a different title by the time it gets there). An updated version of Ben Thompson's book 'Sunshine On Putty: The Golden Age Of British Comedy, From Vic Reeves To The Office' (Harper Perennial, £8.99) is out now