It is not your average household. Mum and dad sit on the sofa drinking hooch like it is an Olympic event. Their two teenage children bicker for England. Then there is blind Aunty Hayley in the corner, all Chaka Khan hair and sludgy brown cardigan. Oh, and there are cameras all over the lounge.

No, this is not a new reality TV show, this is Shepperton Studios where the bizarre song, dance and fantasy “comic memoir” Beautiful People is being filmed. The story is based on the best-selling autobiography of Simon Doonan, who grew up in boring Reading (sorry, Reading) dreaming of glamorous city life. There are echoes of Hanif Kureishi’s Buddha of Suburbia in the yearning for escape, a flicker of The Naked Civil Servant in terms of sexuality, while the sight of happy, hoofing schoolkids hints at Billy Elliot.

For Doonan the dream came true. Another book, Confessions of a Window Dresser, has been optioned by Madonna, and he has not given up the day job he yearned for in his grey bedroom. Doonan is creative director of New York department store, Barneys, and each episode of Beautiful People – scripted by Jonathan Gimme Gimme Gimme Harvey – kicks off in modern Manhattan before flashing back to Simon’s semidetached childhood.

While Meera Syal does her share of upstaging as Aunty Hayley and Luke Ward-Wilkinson impresses as young Simon, the series is most notable for Olivia Colman’s breakthrough role as loud, proud mum Debbie. Comedy buffs who know Colman as Sophie from the C4 sitcom Peep Show should brace themselves. While Sophie was bland, brown-haired and passive, Debbie is an in-your-face blonde in 24/7 tight skirt and high heels.

“Can you make sure everyone knows that my hair extensions are supposed to be bad,” Colman explains over a catering-bus lunch. The original book was set in the late Fifties/early Sixties. Here the action is set in the late Nineties but Debbie retains a retro look. “She married young, decided what her look was and is sticking with it. Simon’s mum had a pinned-up Hollywood hairstyle throughout her life. We’ve been loyal to her memory but gone for something more Parisian Left Bank.” Well, Left Bank-meets-Berkshire-High-Street anyway.

For the down-to-earth 34-year-old, taking the role was an easy choice. Colman adores Peep Show stars David Mitchell and Robert Webb, but there was a niggle that she was becoming too closely associated with them, teaming up with them on various projects and generally becoming their go-to name whenever they wanted a funny woman.

This year she took stock and she will not be in their next BBC series: “My agent suggested I should be open to more different things. There were tears when that decision was taken.” Peep Show-philes can relax. She will return after the last run ended on a cliff-hanger, with Sophie pregnant. “I’ll always find time for Peep Show,” she smiles, as writer Jonathan Harvey says scurrilous things about Liza Minnelli behind us.

Her relationship with Mitchell and Webb dates back to Cambridge, though she wants to put the record straight. People have assumed she was a Bright Young Thing; the truth is cloudier. Her family comes from Norfolk where “granddad was a postman called Pat” and her parents “did up houses”. She went to teacher training college in Cambridge and joined Footlights, but after one term dropped out and never handed her Footlights membership card back. “I was actually working as a cleaning lady when I met David and Robert.”

Eventually she went to study drama at Bristol Old Vic before reuniting with the duo. There was never any offstage romance. “I was slightly in love with both of them, but nothing ever happened”, probably because she had met her future husband, the aspiring writer Ed, by then. They currently live in South London with their two small sons and have a very non-celeb lifestyle.

Her career is certainly taking off. Last year Colman worked with Shane Meadows and Paddy Considine on the cult film short, Le Donk, in which Considine played a hapless roadie and she was his long-suffering wife. She is now due to star in a serious spin-off written/directed by Considine. “I’m beaten and raped by my husband and finally I retaliate. It’s really exciting.” On the lighter side is an ITV comedy, Mr Eleven, due to go out in 2009, in which Colman plays Bionic Woman Michelle Ryan’s geeky sister.

There have, however, been less fulfilling projects. In 2006 she co-starred with Robert Webb in the British rom-com Confetti. They played naturists, which meant appearing nude. Colman has previously said that this was the “worst experience of her life” and does not want to talk about it, except to say that it was a “steep learning curve”. Since then she has been more cautious about scripts.

Beautiful People, by contrast, is clearly a happy shoot. The cast bonded when Colman arranged for a mobile blood donor unit to visit the set. A friend recently had leukaemia and, following a bone marrow transplant, is now recovering. Colman is a passionate proselytiser, persuading everyone to register: “It takes a minute and can save a life.”

One thing has been puzzling me all day though. How come Hayley is the family auntie and yet is clearly of Asian descent? Meera Syal pops into the catering bus for dessert and sheds some light. “Debbie was working as a barmaid and met Hayley when she was drunk and brought her home and adopted her. I relate to that because we had all sorts of aunties and uncles in our house when we were growing up.”

And that may explain the appeal of this clan that puts the Gallaghers in Shamelessin the shade. The Doonans might appear dysfunctional, but they are probably no more eccentric than any other domestic set-up. Just because you do not burst into Broadway tunes like Simon or have boxing matches in the street like Debbie does not make you any more normal. Maybe the Doonans are an average household after all.

Beautiful People, Thur, BBC Two, 9.30pm

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