David Mitchell and Robert Webb are an unlikely source of controversy. In person, the comedy duo are so polite, they’re charming. Their acting is warm and naturalistic; their self-penned sketches are witty, with a faintly surreal twist. Yet the past few years have seen them championed by Ricky Gervais, in a furious comedy-awards acceptance speech where he berated the organisers for ignoring their sitcom Peep Show, while sections of the web are aflame at their appearance in Apple’s new Get a Mac campaign.

The ads – in which Mitchell plays a hapless and dreary PC while Webb constantly trumps him as an urbane, accommodating Mac – have taken them from comedy’s next great discovery to mainstream faces. Ironically, they agreed to the campaign only because it wouldn’t be on TV, and so would not eclipse their sketch-show and sitcom work. “The fallout from the ads wasn’t so much ‘Why are Mitchell and Webb doing this?’, but more a holy war between PC and Mac users,” says Webb, sounding slightly baffled.

Mitchell agrees: “It’s odd that people don’t seem to realise basic rules of advertising. Apple paid for the ads, therefore they are not terribly likely to show the PC in a positive light. But you have all these people with very little to do at work ranting away online. The comments stop at 5pm every day.”

Mitchell admits to being slightly worried at the ubiquity advertising can bestow: “I’d hate the backlash to start before the lash itself had finished.”

The twosome met at Cambridge during a Footlights production of Cinderella in 1993. Webb, being a year older, was part of the Footlights crowd; Mitchellwas thefirst-term newbie. They teamed up and beavered away on the live comedy circuit for almost10 years,earning scant recognition fromall but die-hard aficionados until they were cast in Channel 4’s Peep Show in 2003. A flat-share comedy, it has a cute trick of using the camera as a character’s eyes – allowing a voiceover to ramble through their thoughts. It was critically well received, but ratings for its first four series stuck resolutely around 1.3m, despite Gervais calling it “the best sitcom since Father Ted”.

Years as the best-kept secret in comedy beckoned, until the BBC commissioned a radio sketch show, That Mitchell and Webb Look, which transferred to BBC2 last autumn. Its skits include an incomprehensible spoof quiz show called Numberwang.

Look’s ratings quickly peaked at almost double Peep Show’s, and a national tour found them playing to audiences “who actually wanted to be there”, says Mitchell, a little incredulously.

Now everything is exploding around them. Over the next month, Radio 2 will broadcast the pilot of their sci-fi comedy, Daydream Believers, in which Mitchell plays a tetchy sci-fi writer who finds Webb continually interrupting, and ends up incorporating their mundane conversations into the adventures of the alien Baron Amstrad and his constantly interrupting android companion, Info.

They will also star in Magicians, a film about a magic double act that splits when Webb is caught having an affair with Mitchell’s wife – who dies that night in a horrible “sawing a girl in half” accident. Subsequent commercial failure forces them back together, where they deliver their routine through gritted teeth. Meanwhile, the fifth series of Peep Show has been commissioned, and there are sketches to be written for the next series of Look, which airs in the autumn.

You get the feeling that the pair are almost waiting for the universe’s brutal Candid Camera crew to appear and reveal that the past 12 months have been a gigantic cosmic prank. “If you had told me five years ago that any of this would have happened, I really wouldn’t have believed you,” Webb says, shaking his head.

“I’m very pleased, but constantly afraid,” Mitchell says. “All I’ve ever wanted to be is a comedian on TV, and now I am. I think we’re both quite ambitious, but also quite lazy. That’s the thing we find within ourselves. We dread the thought of something f***ing up because we haven’t worked hard enough. The next few years will be about clinging on in terror, hoping that at some point we’ll become a fixture, rather than vulnerable outsiders.”

They are so cautious and curiously analytical that they have made a conscious decision to stop socialising with each other. They know their comedy history and are aware of the risks of conflict with writing and performing partners.

“Of course we don’t avoid each other in a stupid way,” Webb scoffs. “We’ve got the same friends in the same part of London, like some horrible, cloying Friends-style social scene, so it would be crazy to walk out if the other comes in.”

They are even cautious with their adland millions – although they hasten to add that millions is so the wrong word. “We’re doing all right,” says Mitchell carefully. Webb got married at Christmas, “in a slightly more extravagant way than I might otherwise have done”.

Mitchell adds that he “has it in mind that if I have another couple of good years, I’ll move. I’ll buy a small house rather than the small flat I’ve got. I’d like to be able to play table tennis where I live. That’s as far as my imagination stretches; that’s my dream”.

NonPC humour

The Get a Mac campaign was created and scripted by Apple’s US advertising agency, TBWA. In America, the Mitchell and Webb parts are played by John Hodgman and Justin Long. Hodgman is one of the resident experts on The Daily Show, Jon Stewart’s satirical sketch programme, while Long is a not particularly well-known actor.

The Hodgman and Long commercials are shown across North America and Australasia, using similar scripts to those in the UK. In “Work v Home”, Mac describes how he enjoys doing fun stuff, such as podcasts and movies. PC claims that he also does fun stuff, such as time sheets and pie charts. Mac says it’s difficult to capture a family vacation using a pie chart, so PC pulls one out, coloured in different shades of grey.

In the USA, areas represent “hangout time” and “just kicking it” time, while in the UK, one area represents “shenanigans and tomfoolery”, and another “high jinks” – which is further divided into “monkey business”, “capers” and “just larking about”. On such differences entire cultures are created.

In Japan, the ads are played by the comedy duo Jin Katagiri and Kentaro Kobayashi – known as The Rahmens – who gently mock the formality of their culture in a TV series called The Japanese Tradition. Skits on YouTube include beautifully observed advice on eating sushi and tips on the correct bow for a product recall.

The Japanese ad scripts are almost unrecognisable, because bragging about your strengths is considered stupid and rude. Instead, the Mac shows class by remaining sophisticated, humble and controlled in the face of the PC’s increasing overconfidence and excitement. The punch lines, it’s safe to say, are lost in translation.

Editor's choice

• The 100 Best Films of the Decade
• 70 facts you didn't know about Marvel
• The 50 Biggest Movies Of 2010