Peter Serafinowicz was tired of forever playing the stooge, so he posted a sketch of his own on YouTube. Now, with a little help from Alan Alda and Sly Stallone, he's got his own TV show. He talks to Andrew Pettie. Portrait by Eva Vermandel

Peter Serafinowicz wants to be big. In the most thuddingly literal sense, of course, he already is. The 6ft 5in actor and comedian is huge – a looming, booming bear of a man, with a chest like an oil drum and the voice of a chain-smoking double bass. As he strides towards you, giant palm outstretched in welcome, it's like being accosted by a minor Norse god.

In theory, Serafinowicz's cv should be just as memorable. He was born in Liverpool in 1972 and educated at St Francis Xavier's secondary school. Like many home-grown comedians, his first major break came on the radio, where he starred in The Knowledge, a spoof documentary about the music industry broadcast on Radio 1.

After transferring to television, he won roles in a raft of well-received sitcoms. He appeared alongside Steve Coogan in I'm Alan Partridge, with Simon Pegg in Spaced, with Phil Cornwell and Kevin Eldon in World of Pub, with Dylan Moran in Black Books and with Martin Freeman in Simon Nye's Hardware. He popped up in the pilot episode of Little Britain, has performed several skits for Comic Relief, and, in 2002, co-wrote and starred in two series of Look Around You, a scrupulously recreated parody of science and schools programming from the 1970s and 1980s.

But Serafinowicz is probably best known for starring in two multimillion-dollar movies. He played Simon Pegg's boorish, zombified flatmate, Pete, in the surprise Brit-hit Shaun of the Dead, and, somewhat bizarrely, supplied the voice for Darth Maul in George Lucas's Star Wars prequel The Phantom Menace. At the time, says Serafinowicz, he was doing ominous, gravel-voiced movie trailers of the 'Can you smell the taste of fear?' variety. His agent suggested he audition for the role of the glowering Sith Lord and Lucas liked (and apparently laughed) at what he heard. 'I don't really say much in the film,' says Serafinowicz. 'Mostly, I watched lightsaber battle scenes and did grunts and growls while George Lucas watched from the couch.'

For such a large and striking-looking man, Serafinowicz is also an unexpectedly versatile impressionist, performing with a roster of ?'acts', including Sly Stallone, Nicolas Cage, Michael Caine and Robert De Niro. When we meet on the set of his new television project, his thick black hair is lacquered to his scalp after a long morning spent in Beatles' wigs and freakish prosthetics.

Later, on my way out, I pass a burly man with bushy sideburns and a faintly Edwardian air sitting in reception. I nod politely, as does he. It's only as the lift doors clang shut that I cotton on: the hairy Edwardian was Serafinowicz himself, waiting incognito to film his next scene.

Despite all these distinctive faces and voices, few people can identify Peter Serafinowicz by name. Over the past seven years, he's been the very-nearly man of British comedy: forever the flatmate, the sidekick, the bit-part player you always chuckle at but can't quite place.

All that will, it is hoped, change on Thursday, when the opening episode of his six-part sketch series starts on BBC2. Serafinowicz's first crack at solo stardom is called, in a long overdue act of self-promotion, The Peter Serafinowicz Show, and he got it thanks to Alan Alda, YouTube and a failed audition.

'The whole series sprung out of a single skit I made to get a part on [West Wing creator] Aaron Sorkin's Studio 60 on the Sunset Strip,' he says. 'The Oscars were coming up and it was the top story on every TV channel in LA. [Adopts oily Californian twang] "Never mind the war in Iraq – it's the Oscars!" So with some basic video equipment and virtually no money, we shot this three-minute spoof piece about the Oscars that I could use as a showreel for my audition.'

The result was O! News, a pitch-perfect send-up of the rolling celebrity news froth pumped out by the likes of the E! Entertainment channel. Serafinowicz plays 90 per cent of the characters, including the tangerine-tanned, rictus-grinning anchor Kennedy St King and any number of A-list actors supposedly vox-popped on the red carpet. His Alan Alda ('I think it's ludicrous, preposterous... I mean the whole thing is ridiculous') is superb. Meanwhile, George Michael speaks out about the pressures of fame – 'It's got so bad I've got to meet my boyfriend on a space station' – and Sly Stallone spills the beans about the latest Rocky movie: 'Rocky is actually dead at the start, but Paulie finds a serum that brings the body back to life – then the corpse has a fight with Apollo Creed's ghost...'

Serafinowicz's showreel didn't get him the part. But he decided to post the O! News short on YouTube anyway, just to make people laugh and see what they made of it. 'The reaction was phenomenal,' he says. 'I can't quote the exact figures, but I know more than 100,000 people watched the video in the first two days it was up there.' On the back of the astonishing word-of-mouth popularity of that one skit, recorded for an audition he didn't get, the BBC handed Serafinowicz his own series.

In terms of comedy commissioning, he is a pioneer. 'I know it almost sounds like a cliché to say it, but the internet is revolutionising comedy,' he says. 'Even in 2002, when we were making Look Around You, it would take months, even years, to turn your ideas into something people could sit down and watch. Now you can have an idea for a sketch, film and edit it yourself and post it on the internet the next day, where thousands of people will instantly tell you whether they think it's funny.'

At first, The Peter Serafinowicz Show was going to be an extended, expanded version of O! News. But it quickly gestated into a pic'n'mix sketch show, swerving between one-off gags, recurring characters, bizarre costumes, celebrity impersonations and spoof musical numbers. So, if Little Britain was known for its contagious catchphrases and outlandish caricatures, what defines The Peter Serfanowicz Show? 'Silliness. Most of it's just plain daft, completely stupid,' says Serafinowicz. 'I don't want there to be anything cruel or sneering about my comedy.'

The Monty Python team are a major influence, Serafinowicz says, and you can see snatches of their poker-faced surrealism in his show. Sample sketches include a late-night pirate chat-line ('Would you like to have a live one-on-one personal chat with a pirate? Our dirty pirates are waiting for your call') and a Sherlock Holmes character so aroused by the act of solving a mystery that he feels compelled to make love to a startled and unconsenting Watson ('This simply isn't on Holmes, I mean really'). Even closer to the bone comes a Simon Cowell reality show send-up called 'America's Best Male Prostitute'. (Serafinowicz as Cowell, zipping up his flies: 'You are by far the worst male prostitute I've ever had.')

Although Serafinowicz is indisputably the star of the show (the opening credits show him tap-dancing in front of his own name lit up like a Broadway musical), he has sensibly mined a bulging address book of comedy connections for advice and second opinions. He is good pals with Simon Pegg, Nick Frost and the Shaun of the Dead writer/director Edgar Wright; every Thursday, they used to compete in the same quiz team at the Shepherds pub, in Highgate, north London. His brother-in-law is Graham Linehan, the creator of Father Ted. His girlfriend, who also appears in the series, is Sarah Alexander, star of Green Wing, Coupling and Smack the Pony.

They were all shown sketches as they were filmed. 'It's no good everyone slapping you on the back and telling you how hilarious you are,' says Serafinowicz. 'You want to find out what bits they hated, what jokes they didn't get, so you can go back and tweak them.'

With this crack team of comedians egging him on from the wings and an expectant audience already posting their excitement on YouTube – 'Can't wait for the series to start', 'Love that man!' – Serafinowicz seems set to finally become a household name. His jokes certainly have the desired effect on his younger brother, James, who also acts as the series' producer. After the interview, James invites me to sit in on a rehearsal of a musical number in which 'Ringo Starr' sings, or rather drones (as a Liverpudlian, Peter can impersonate every one of the Fab Four with subtly differentiated brilliance), his 'sadly overlooked' version of Shirley Bassey's Goldfinger as 1960s backing dancers sparkle to and fro in sequined miniskirts.

James, wincing and spluttering at the inspired awfulness of it all, can barely contain his giggles. 'I genuinely find just about everything Peter does, both on and off camera, very, very funny,' he says. 'He's been behaving like this – doing stupid impressions, having daft ideas – ever since we were kids. In fact, some of the skits I remember him performing for the family at Christmas are now in the series. We can't quite believe the BBC is paying to put all this stuff on the telly.'

• 'The Peter Serafinowicz Show' starts on Thursday, 9.30pm, BBC2

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