Before she was Maggie in Extras, Ashley Jensen appeared in the background of a number of television dramas. She was there, or thereabouts, in Taking Over the Asylum and The Tales of Para Handy. She was a series regular in Bad Boys. She did The Bill, Rebus (the John Hannah version), Silent Witness, Casualty, Two Thousand Acres of Sky and City Central (three series of it). She was a lady of the chorus in the Mike Leigh film Topsy Turvy, and played "a paedophile's wife" in EastEnders, appearing in five episodes as support to Forbes Masson.

All of it was decent work, and none of it was the sort of thing to get you noticed in the supermarket queue. Last year she featured, as Scottish actors must, in Taggart, playing a newspaper editor called Agnes. "I was offered a dead body in Taggart 14 years ago, and there were no lines, and I turned it down, and I thought I'd offended somebody."

And then there was Extras.

Just before Christmas, Jensen had a very unusual week. It started with an appearance on the Jonathan Ross radio programme and ended on the Jonathan Ross television show.

In between, she won Best Comedy Newcomer (at the age of 36) and Best Television Comedy Actress at the British Comedy Awards for her performance as Maggie in Extras. There was also a day of interviews and photoshoots for her latest drama, Eleventh Hour. Jensen sounds half-bewildered as she recounts this schedule, between mouthfuls of fish-finger sandwich at her local pub in west London.

"I'm under no illusions, " she says. "I was only on Jonathan Ross because Scarlett Johansson dropped out. It's like my first job at the Citizens' Theatre in Glasgow: I was only there because I looked so young and it was cheaper than employing a child and a chaperone."

Famously - she told the anecdote on Ross's TV show - Jensen celebrated her awards by sneaking out of the ceremony and buying a cod in a baguette from a chip van near Waterloo.

A week later she still seems more interested in discussing this midnight snack than contemplating her success: "He said, 'I've finished doing the chips but I could do you a cod, ' which made me wonder how he could do a big cod but he couldnae do a handful of chips. But it was the best big cod in a baguette I've ever had. It was about that long." She spreads her hands a yard apart. "It was ridiculous. With tomato sauce up it." Not long after the award ceremony, Jensen was asked whether she would front National Potato Week. It was an offer she did not pursue. "I was like, 'What do you mean, front a potato?' I thought, no, I'm not that interested in fronting the chip week.

What were they thinking?"

Eighteen months ago I interviewed Ricky Gervais, the writer and comedian, who explained he had decided to follow his wildly successful sitcom The Office with a low-key comedy called Extras. Originally Gervais wasn't going to act in the show, but he changed his mind when the character of Andy Millman became too neat a fit.

Andy is an extra on television and film sets, always hoping, but never managing, to say a line on camera. Gervais compares him to Bilko in The Phil Silvers Show, and Fletcher in Porridge. He is a man who can issue a one-liner in the face of adversity. "This isn't a guy doing high-fives and being loved, " Gervais told me then. "Bilko: great one-liners, but he's a man surrounded by idiots. He doesn't win. Fletcher in Porridge: great one-liners, you think he's a winner, but he's not, he's incarcerated and he's got to look after Godber. These people aren't winners. They're plagued with wit."

Gervais didn't mention the character of Maggie at the time, but he did say something that, in retrospect, reveals the architecture of Extras. The rules of comedy hadn't changed since Laurel and Hardy, he explained. He wasn't interested in disjointed jokes, puns or surrealistic rants. He liked character. He liked comedy to resonate. Most modern comedy, he said, didn't: "I don't go to bed with a smile on my face, but I remember the look on Olly's face."

"It would have been easy for him to write another thing for himself, " says Jensen now, "but it really was a double-act that he wrote. It was very Laurel and Hardy-esque." On the first day of shooting, Jensen, as Maggie, had to tell Samuel L Jackson that she thought he was great in The Matrix. Jackson replied that he wasn't in The Matrix. Maggie was insistent, while her horrified friend Andy looked on. No, said Jackson, Laurence Fishburne starred in The Matrix. "And just as we walked off into the distance, Andy said, 'Another great day being friends with you.' It was just like, 'Another fine mess you've got me into' and I thought, 'God, it is Laurel and Hardy.'" And Jensen is Laurel?

"Only because I'm slimmer." She laughs. "And he's the kind of grumpy buffoon."

Typically, she makes no mention of her own contribution to Extras. Or the fact she now shares an agent with Jackson.

Inmost British sitcoms, Maggie would have signalled her own stupidity with gurning and exaggerated gestures. In Extras, that would have been a problem as it would have been out of tune with Gervais, an actor in the Jerry Seinfeld mode: he doesn't act so much as deliver his lines while standing upright. Jensen, though, is effortlessly natural, to the extent that she doesn't seem to be acting at all. When she makes a fool of herself it's hard not to empathise.

"People ask, 'Is it true to life, is it like being an extra?' I think it goes deeper than that. It could almost be set anywhere. It's actually just about humans, about people. Everybody wants to be acknowledged or loved or accepted in some way, whether that's down to 'I like your jumper' or 'You did a great fish-finger bun' or 'You're so beautiful I've fallen in love with you' or 'You're so talented I'm going to give you a line in this show, Andy Millman.' Everybody wants recognition as a human being, so it's almost like the human condition - like a wee microcosm of what we're all about - and I think that's why people can relate to it."

Jensen is popular with women. This might be because of Maggie's ineptitude in the dating game, or it could be because of her habit of blundering into embarrassing situations and saying the wrong thing. "We all put on this facade and pretend we're much cooler than we are, and we're all the same underneath, basically. The thing about Maggie is that she's not particularly ambitious, and it's not a bad thing. She doesn't get brownie points for being a nice person, which is what she is. Things like that don't count in today's society. You've got to be a famous person, or you've got to wear designer clothes. You've got to do something.

But to be a decent person, people don't really acknowledge that."

The relationship between Andy and Maggie is also interesting. They are friends - no more, no less - which, as Jensen points out, "doesn't really happen very often in television. Usually there's a wee sexual undercurrent or an unrequited love. But they like each other, don't they?

They make each other laugh. Despite their awkwardness with other people, they seem quite comfortable and easy with each other."

Ashley Jensen has many voices, and her conversation is coloured by comic accents and mocking asides. But there is one funny voice that seems to appear more frequently than the others - more than the self-important Actor or the insincere American. It is the voice of a Scottish wifey, mocking anything that threatens to sound pretentious or fancy-dan. Without getting all psychological and incurring the disapproval of this nagging voice, it is the sound of a grounded childhood in the Dumfriesshire town of Annan. "There is a Scottish mentality I feel quite proud to have, which is that, well, it might not last, " says Jensen. "It's quite a fickle business that we're in. You can be flavour of the month - all of a sudden you're getting invited to things willynilly - and the next minute somebody else has appeared and you're not being interviewed or photographed any more.

"I feel comfortable with me, and who I am, so I just feel it's great while it lasts. But there's nowt as queer as folk, and it can all go pearshaped. I hope it won't. I hope I still manage to do something else." She collapses in laughter, and the chiding voice chips in: "Och, ye can take the girl out of Scotland but . . ."

As a child, Jensen never had any doubt she would be an actor. "There was never much question about it. It was a statement. I nearly became a drama teacher after my three years at drama school. But then I thought: I don't want to fall back on it. I want to be able to [daft dramatic voice] follow my dream. I wanted to take a crack at it. I didn't want to get to my old age and go, 'I wish I'd tried that, I wonder what would have happened.' And I'm glad I did try it."

It was a happy childhood. She was "one of these wee children that was into everything".

She was in the Guides, striving to get badges.

She did short-distance running, even appearing at the Scottish schoolgirls' championships at Meadowbank. She stopped running because she felt lonely going away with the running group, who were all boys. But there were other diversions. "I was always doing my wee amateur dramatic club and my Duke of Edinburgh award. I got the Gold." She went to Holyrood Palace to collect the award, but didn't meet the Duke. "We met Mr Tunnock of Tunnock's Teacakes. The Duke of Edinburgh never came, so we got Mr Tunnock.

The actual Mr Tunnock:

the big teacake himself."

As a teenager, she says, she had "an interesting sense of style". She laughs.

"Remember banjo players used to wear these little black boaters? I had this little black boater that I used to wear, and a little 1940s tea-dress and a wee pair of Doc Martens boots.

That was me - Mr Tunnock, there you go! And I remember I once went out in my gran's waterproof golfing trousers. On a Saturday night. I thought, 'That's different.'" She was, she concedes, a little unconventional. "I would do things like get Doc Martens and spray them silver and put glitter on them, and have tartan laces. But I wasn't really rebellious. You know how, in the late 1980s, young people wore old men's coats, old men's suits?

I used to wear old men's clothes and teadresses and footless tights. Remember those wee black gym shoes? I've always liked dressing up. As a child, for my birthday, I'd say, 'I would like some face paints and a false nose or two, please.' And then I'd go into my room and do a wee bit of make-up on myself, and come through the house. Wa-hey!" She adopts the flattened voice of an unimpressed adult:

"Very good."

Acting was never about fame for Jensen. It was an end in itself. She studied drama at Queen Margaret College in Edinburgh and acted with the 7:84 company, appearing in a male fat-suit with David "Doctor Who" Tennant in The Resistible Rise of Arturo Ui.

She was a regular at the Tron in Glasgow under Michael Boyd, and at the Traverse in Edinburgh. "I'm glad I've had the career that I've had, " she says. "I've done small-scale, mid-scale and large-scale touring; new writing, classical theatre."

Until Extras, her most intensive encounter with commercial popularity was the Rab C Nesbitt theatre tour, "on the tour bus, with Rab himself. And Mary Doll". The tour began at the Blackpool Opera House, to a crowd of 3,000, and ended at the Hammersmith Apollo in London. Jensen played two characters:

Rab's first girlfriend, "wee Izzie Niddrie", and then "a blousy old slapper that Jamesie got off with". She smiles at the memory. "You'd get people coming dressed up as Rab C Nesbitt, so Gregor [Fisher] would get this sweaty bandage that he'd been wearing throughout the show and throw it out into the audience. It was like a big rock gig. It was brilliant."

Jensen's career built steadily until she found herself being offered more work in London and moved south. She is keen to stress, however, that this was not a rejection of her roots. "I didn't go [wifey voice again] 'I'm washin' ma hauns o' Scotland noo.'" She pauses for a moment. "And it seems to be different now for people leaving drama school; different from how it was when I was there. You served your apprenticeship. You did community theatre, you went to village halls and you played to two old ladies and a greyhound. It would be cold and you'd put the set up and then you'd take it down and you'd go and stay in some dank guest house where you got cold porridge in the morning, and then you'd drive to the next place. But I wouldn't change that for the world. It was a great life."

Jensen may sound as if she is always preparing for disappointment, but her self-mockery is a kind of modesty. She recently went on holiday to California with her "gentleman caller" - the actor Terry Beesley, with whom she lives - and, between trips to Vegas, Death Valley, Yosemite and San Francisco, she managed a couple of meetings in Los Angeles.

"We stayed at the Mondrian hotel. Everyone was like [whiny American voice] 'You gotta go to the Mondrian.' It's all Philippe Starckdesigned. Now, I prefer something a wee bit cosier myself. A wee bit more sumptuous. But it had this amazing bar, the Skybar, and because it was set in the hill it was all glass walls around it, and you could lie back on these big mattresses supping margaritas, looking over the lights of LA. But because it was LA I felt like a mutant. All the people were tanned and very blonde and honed. [Nasal American voice] 'My name's Kelly, how can I help you?' They were all like that. Everybody was involved in the media or wanted to be an actor. Terry and I were like, 'C'mon, we'll just go and sit in the corner.' I had to work up to going in the pool. It was like, 'No, I can't go yet, I can't go yet. There's too many body beautifuls round the pool. Then it was like, 'Okay,

hold your stomach in, whip the sarong off, in you go.' We didn't hang about for very long."

The meetings went well, but Jensen decided not to talk about them back home, on the basis that they would only be meaningful if she got some work from them. Her discretion was thwarted when Samuel L Jackson announced at the comedy awards that she had signed with his agent. "I was like, 'Okay, so I don't think I'll be keeping that quiet for much longer.'" The second series of Extras follows later this year, but Jensen can be seen first in Eleventh Hour, an ITV thriller. "Patrick Stewart plays a government science adviser who travels around the country, troubleshooting sciencebased problems. People have gone, 'Is it like Doctor Who?' Well, no, because it's fact rather than fiction. And it's not Mulder and Scully either. It's based on things like human cloning and climate control. Because of his work he has noised up people around the country and requires a close protection officer - a bodyguard.

In the form of me."

Jensen notes the expression of incredulity on my face. "That's what a lot of people do, " she says. I ask whether the point of the drama is that she [5ft 3ins, blonde hair, crocheted clothes] makes an unlikely minder. "No. You're meant to take me seriously." But she's not tough. "Ah, but I can pull a serious face, and I get to hold a gun. They didn't want to go for the obvious, a sterner-looking person - although I can look very stern when I'm not smiling. 'See with my hair pulled off ma face and a wee serious suit . . . ' And it's a double-act where he kind of resents me being there because he thinks he doesn't need a bodyguard, and I resent being there because I feel he's thwarting my career opportunities for promotion within the police, although that's all subtext."

Is it because he's being looked after by a lady? "Interestingly, that doesn't come into it, which is quite nice. It's not obvious sexism stuff. She's very much a kind of . . . see, I'm embarrassed at talking about it seriously, because you've laughed at the thought of me being . . . she's a woman in a man's world. She can hold her own. Anyway, yeah."

Is it good? "Apparently." She laughs.

By now, Jensen has to leave. She has to get to the dry-cleaner's before it closes, and calculates she can do this if she does her final interviews on the phone in the ITV car. Before she goes, she squeezes in another flurry of selfdeprecation, saying that on the rare occasions when she's recognised in the street, it is invariably because she has one of those faces people think they recognise. "They say, 'I know what it is, you look like my neighbour when I was growing up in Troon.'" I ask her about her inner wifey, and the Scottish habit of preparing for failure even in the midst of success. "I think that's all right, though, " she says, slipping into the voice. "Aw, you're getting kerried away by your own selfimportance. Steady the bus." She pulls a perfectly bewildered Stan Laurel face. "My wee heid's throbbing from talking about myself."

Eleventh Hour begins on January 19 at 9pm on ITV1.