Anywhere else, it would be a cause for celebration. Later this month, a debut feature is to be released by the director of one of Britain's most popular TV comedies. Bafta-nominated for his work on BBC2's The Mighty Boosh, Paul King is also an award-winning live comedy director – and his new film Bunny and the Bull was selected for both the Toronto and London film festivals. Here, then, is a cheering tale of a home-grown talent making his way in cinema, right? If only it were that simple. "There's a pack mentality with British comic films to go, 'What a heap of shit!'" says King. "Your worst nightmare is, 'Oh God, I just hope my film's not one of those …'"

One of those? Does he mean Sex Lives of the Potato Men, the inglorious 2004 sex comedy that the Times branded the worst film ever made? Or this year's Horne and Corden vehicle Lesbian Vampire Killers, which one critic (in a review that began, "The history of British cinema is strewn with disastrous misadventures by TV comics …") branded "witless and consistently abominable". There are plenty of other examples to choose from. But what would that prove? That British film comedies – particularly those that joined the goldrush following Edgar Wright and Simon Pegg's hit zombie spoof Shaun of the Dead – are uniquely awful? Or that there's a cultural cringe-factor at play that leads, according to Sam Bain, co-writer of the Channel 4 sitcom Peep Show and the Britfilm flop Magicians, to British cine-comedies "getting slammed in quite an emotive way"?

King finds those recent "high-profile stinkers" easy to dismiss – "You put lesbians and sex in the title, the impression is not one of high aspiration," he points out – but the general air of underachievement that surrounds UK film comedy is harder to deny. "We've got a good TV track record," says King. "But it doesn't usually translate to the big screen." That failure can be exaggerated, and often is – notably by Ricky Gervais, who rarely misses an opportunity to denounce the "terrible, Lottery-funded, tacky shit" that passes for UK film comedy. But even insiders admit there's a problem. As Simon Farnaby, standup comic and star of Bunny and the Bull, says: "Withnail and I was made in 1987, and it's still the standout British comedy. As far as British comic film tradition goes, there doesn't seem to be one."

Bunny and the Bull is being sold, inauspiciously enough, as "Withnail and I for the mentally ill" – presumably because it's about two male friends, one of whom is mired in agoraphobia and post-traumatic stress. But the more likely comparison is with The Mighty Boosh, from which King lifts his magical visual style. The European road trip taken by Bunny (Farnaby) and Stephen (Edward Hogg) plays out wholly in the latter's imagination, using Oliver-Postgate-meets-Jan-Sˇ vankmajer backdrops, livestock made out of cutlery and a fairground constructed from the cogs of a carriage clock. This is King cocking a snook at the cheap aesthetic of Britfilm comedy. "We have such an inventive art and theatre heritage," he says, "so it's annoying that 90% of British film is set on a council estate." According to King, British filmmakers "hide behind their budget. 'We didn't have much money so we shot it in my mate's living room …' But I know what you can do for very little, and I wanted something with visual drive."

The resulting animations will delight Boosh fans – perhaps more so than the film itself, which operates in a different register to the TV show. An introspective indie tragicomedy whose comic element slightly misfires, Bunny and the Bull may feature Julian Barratt and Noel Fielding – but their conspicuous cameos emphasise the film's distance from its small-screen source. "I know some people will go wanting to see Mighty Boosh the Movie," says King. "But we're going to not give them exactly what they're after." (Barratt and Fielding recently announced plans for their own Mighty Boosh film.)

When comedy talents take on the cinema, they face a choice. Do they just scale-up their small-screen success? Or try something else? King chose the latter. "What Simon Pegg did with Shaun of the Dead was go, 'This isn't [Channel 4 sitcom] Spaced. It's got the same people in it, and if you liked Spaced, you might like it. But it's a different proposition.' That's a better way to go than making Rising Damp the feature-length episode." Time was, the League of Gentlemen's Jeremy Dyson would have disputed that. In 2005, he wrote a piece for this paper championing the sitcom spin-offs of the 1970s, when On the Buses outsold Diamonds are Forever at the UK box office. But after the disappointing performance of the film Dyson was then promoting – The League of Gentlemen's Apocalypse – he now sees the TV tie-in as trickier cinematic territory.

"We were naive," says Dyson. "Doing a comedy show on BBC2, you focus on: is it good? But film is capitalism in its brutal form, and it's about: how are you going to get an audience? We'd never thought like that before." Were he to make another film, says Dyson, he'd "plug into something, like Shaun of the Dead did, that has universal appeal. Approach it like one of those low-budget horrors which are guaranteed to recoup money." The days of the surefire TV-to-cinema hit are gone, he says. "Things are more atomised now. On the Buses was getting 20 million viewers. A comedy show is now doing well if it gets four or five million."

One such comedy is Peep Show, whose writers Sam Bain and Jesse Armstrong scripted Andrew O'Connor's film Magicians in 2007. Like King, they chose to distance themselves from their TV series. But then "the problem we had," says Bain, "was convincing people that its different style and tone was going to be as good as Peep Show." The casting of Peep Show's stars David Mitchell and Robert Webb confused the issue. Says Armstrong: "The comparison with Peep Show wasn't helpful to us."

In deviating from their TV hit, Bain and Armstrong honoured the received wisdom that different rules apply to film than TV. The failure to observe certain basic principles, runs this theory, has poleaxed many a Britfilm comedy. Says King: "A sitcom is judged by laughs per minute. In film, you're working more to a narrative end." According to Armstrong, "Sitcom is domestic and small-scale, and people enjoy it when it deals with minutiae. That doesn't translate to film well." Similarly, "sitcom characters never change. That's the whole idea. With film, the characters have to change." Recent hit In the Loop, which Armstrong co-wrote, exemplifies the changes required when a sitcom (BBC2's The Thick of It) migrates. "It had more scope, more of an emotional journey," he says. "It had a subject matter – war – that made it suitable for filmic treatment."

But Bain believes those differences can be overstated. "TV writers turning to cinema feel that there are all these abstract rules to obey. It's got to have a happy ending, or a romcom arc. But the only rule in film comedy should be: speak with your own voice, and make up your own rules. In the Loop makes up its own rules, which is why it works so well."

Unsurprisingly, its writer/director Armando Iannucci agrees. The secret, he says, is "not to make a film by committee. The bigger the budget, the more people have a say" – which is why he turned down offers from the US to help fund In the Loop. "You don't want to refuse anyone's money. But you have to be careful what strings are attached. Controllers and producers aren't the funniest people in the world, and yet the decisions about what comedies to make, and how, often rest with them. I didn't want to dilute the film or come under pressure to change it. I didn't want loud music and explosions, and I didn't want a song at the end."

Some of these external pressures apply not just to comedies, but British films in general. Bunny and the Bull star Simon Farnaby has had "a couple of meetings recently trying to get films off the ground. And often what you hear is, 'Where's our transatlantic appeal? Can we put an American in?' And I say, 'Well, it's supposed to be set in Guernsey, so I'm not sure.'" Then there's the film industry's wariness of TV talent. "You do hear sometimes, 'Oh, he's a TV star, not a film star,'" says Bain. "I've heard that in a few meetings with film companies. I don't know what it means."

But in other ways, comedy is uniquely vulnerable to the culture of the committee. For a start, comedies are hard to pitch – on paper, if they're any good, they probably sound ridiculous. And "everyone has an opinion about comedy," says Iannucci. "Which is fair enough, because we all laugh or don't laugh at things. But others may not have as good judgment as those who actually make comedy." The actor and comedian Omid Djalili is currently making The Infidel, a comedy about a British-Asian Muslim who turns out to be Jewish. And "the main challenge David [Baddiel, the writer] and I encountered," Djalili says, "is that we're standups and we have a specific idea of what's funny. And we're working with people from the film world who don't think the same things are funny." The result: endless finicky negotiations over each joke.

But a far bigger problem than lack of autonomy, Djalili says, is lack of funds. "You can't get away from the fact that it will look like a cheap British comedy film," he admits of The Infidel, despite his faith in the film. "We just didn't have money for big sweeping crane-shots. We couldn't afford the 50 more extras we needed." Several of the writers and directors I spoke to have worked on films without taking a fee. "You can't pretend that doesn't impact on the process," says Dyson.

That impact is to make a tough job tougher. Making a film is "incredibly difficult", says Dyson. "On telly, you can recover from a duff sketch. On film, anything that isn't great is amplified." And whereas TV is a protected environment, says Sam Bain, "in multiplexes, you'll get one British film competing with seven or eight American ones. It's as if every British sitcom had to go up against Friends or Seinfeld." Our comedies too often look naff by comparison. "People – and critics as well – feel like film is this big pedestal," says Bain. "They'll forgive a TV show, but they won't forgive a film."

Why are we surprised, then, when comic talents take time to adapt to this world and to master the movies? It's revealing that some of the best comic filmmakers – Bruce Robinson, Bill Forsyth, Mike Leigh – didn't make their name in comedy, with all the pressure to be hilarious that that entails. Instead, they spent years honing their cinematic skills. "When we did Peep Show," says Bain, "we got to rethink it over two pilots, which weren't broadcast, and the whole first series. We got three bites of the cherry. In film, you get one bite, and everyone has high expectations. You don't get any chance to fail. It's difficult to develop a craft in that environment."

Or in an environment in which, after one bad film, you're accused of debauching a nation's film culture. That's just another consequence, says Armstrong, of having a small, unproductive industry. "In Hollywood you get a hundred films, of which five are great and you forget the others. But because there aren't that many here, it's constantly crisis then epiphany. It's 'The British are coming!' then 'The British are fucked!'" The truth is more complex, and less dramatic. "Comic film isn't something we can't do here, or we always get wrong, or it's impossible," says Armstrong. "It's just that it's hard to make good stuff. And we don't make enough films."