Peter Capaldi profile: An alter ego to swear by

You can almost imagine the raging bull of spin, the man who once spluttered "I am the loop", plotting the story. In The Loop, Armando Iannucci's vicious political satire that slings mud in any direction it will stick – bungling ministers, shark-like spin doctors, self-serving civil servants – opened in cinemas on Friday. Its nasty, brutish anti-hero is Tucker, grey of face and foul of mouth, played to terrifying apoplectic effect by a mild-mannered Glaswegian called Peter Capaldi.

Less than a week before release, a spin doctor known in the corridors of Westminster as "McPoison" is exposed for planning a smear campaign against the Tories. Suddenly we're scratching our heads. Which is art and which is life? Who's imitating who?

"I thought we were getting into a dangerous phase where that was no longer zeitgeisty," Capaldi said last week of In The Loop's depiction of his diabolical spin doctor, the star of the film. Inspired by Iannucci's acclaimed BBC series The Thick Of It, Capaldi's character is the only creation that has made the leap to the big screen.

Tucker is one of the great British comic creations of recent years, only quotable in asterisks and as memorable as Tony Hancock, Basil Fawlty, and David Brent. He has been described as "brutal, foul-mouthed, manipulative, psychopathic and war-mongering", and that was just by Alastair Campbell. Tony Blair's communications chief is the man on whom Tucker is widely thought to be based but Capaldi continues to deny the association.

For Capaldi, Tucker is his meal ticket after 30 years in the business and almost 80 film and television appearances ranging from parts in Dangerous Liaisons (as John Malkovich's manservant) and various TV dramas, from the hugely popular The Crow Road to Minder.

"I'm going to be with him as long as they want me," Capaldi has said. "If Malcolm typecasts me it's a fate I will accept happily."

Capaldi, whose home is now in London's Crouch End, with his wife, Elaine Collins, and 12-year-old-daughter Cissy, was born in Springburn, Glasgow, 50 years ago. Iannucci grew up a few streets away, although the pair never met as youngsters. Capaldi attended Possilpark Primary School while Iannucci went to St Aloysius College. Capaldi studied illustration at Glasgow Art School and got his first taste of the acting bug sitting in the audience at the Citizens' Theatre. There was also a spell in a New Romantic band called The Dreamboys with comic Craig Ferguson (currently rivalling Jay Leno on the American chat-show circuit). Capaldi paints himself as a bit of a streetfighter and a rebel in those days. One day he arrived home to find Bill Forsyth chatting with his landlady, a costume designer. So impressed was the director by the 25-year-old that on a whim he cast him opposite Burt Lancaster in Local Hero. It was a random start to a career that has moved on in fits and starts.

Capaldi took his earnings with him to London, and lodged with Ewan McGregor's uncle, Denis Lawson, as he attempted to get some mileage out of his success with Forsyth.

For years, however, nothing lived up to that promising start.

By the late 1980s, Capaldi was lodging with the journalist John Preston, who used him as an adviser on Scottish accents for one of his characters in a script. This experience encouraged Capaldi to have a go himself, and so came his feature film debut, Soft Top, Hard Shoulder in 1993, swiftly followed by his breakthrough win at the Oscars that same year for his short film Franz Kafka's It's A Wonderful Life, starring Richard E Grant and Ken Stott. Suddenly, Hollywood came knocking. Capaldi fancied himself as a writer-director and was commissioned to work on a Miramax screenplay, the proceeds of which bought him a house, before Bob Weinstein summoned him to New York. Picked up by a chauffeur and imagining champagne and success, Capaldi gave the driver a huge tip and strode into the Tribeca office. "Ten minutes later," he recalled, "I was back in the car, dream over. The driver gave me back my tip."

Though he directed another film, Strictly Sinatra, in 2001 it was widely panned. This bitter experience appears to have burnt Capaldi's directing aspirations to some extent, with his long-running on-off pet film project in which Ewan McGregor plays Bonnie Prince Charlie continuing to struggle towards finance and production.

Capaldi's laddish, easygoing characters, however, were carving out a decent television career for him, and then Iannucci unleashed the foaming-at-the-mouth bulldog within at an audition for The Thick of It, in which he read the part of the minister (which Chris Langham went on to play). Iannucci remembers being blown away when Capaldi, who was improvising, suddenly turned nasty and threatened to send him to the bottom of the river if he didn't resign.

He got the part. Since then, he has enjoyed mainstream success playing Charles I in The Devil's Whore and roles in Doctor Who, Torchwood and Skins.

Yet it is Tucker and his head-exploding rage that Capaldi will forever be associated with, especially as his real-life counterparts continue to make the news – in all senses. Last week, Iannucci summed up Tucker's continuing relevance best. "I've always maintained that the Malcolm Tucker figure is a composite of a whole number of people who work in the back rooms, and this kind of proves it," he said of the McBride story. "Rather like Doctor Who transmogrifying from one actor to another, I'm sure that if and when David Cameron gets in, there will be a new sultan of spin in a different guise." That Tucker will remain relevant no matter which party's in government is a fairly safe prediction.

In the same way we see Alan Partidge (another Iannucci creation) every time we see Steve Coogan, when faced with the slender, hollow-faced Capaldi it is hard not to see Malcolm Tucker, despite the sandals and soft voice. "If you're Richard Wilson and people see you in the street they shout 'I don't believe it'," Capaldi has said. "But with me, people ask me to b*****k them." Apparently the one person who he is concerned about seeing the film is his mother. It's hard to imagine a maternal reaction to a line like, "Talk to me that way again and I'll stuff so much cotton wool down your throat it'll come out your arse like the wee tail on the Playboy bunny."

Yet the man could not be more divorced from his venomous creation. "Peter is a very mild-mannered, sweet-natured person who doesn't thrust himself forward particularly and certainly isn't a bully," said his In The Loop co-star, Tom Hollander. "(He's] diffident, confused about why (he's] even in showbiz."

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• Capaldi on spin doctors: "It's a weary, tough job; having day in, day out to go and kick people's arses to get them to shut up and say the right thing."

On playing Malcolm Tucker: "When I play him I feel like I have taken some kind of drug. I try to keep myself on the boil. It's a more technical part to play than people might think. Finding the rhythm of the words is the thing."

On Scotland: "My mother, sister and brother are still in Scotland but they are about the only people I know there. I still come and see them, but I have no social life when I'm there."

"Mark Kermode was clearly hoping that I would be offended by the portrayal of a spinmeister doctoring evidence and manipulating media and politicians in an attempt to force a war that nobody but a few American headbangers really wanted. But I was too bored to be offended." Alastair Campbell, pictured above, on reviewing In The Loop for the BBC Culture Show.