Mommy dearest: Claire Skinner transforms into a monster of a mother

I'm often nice, but I've not been nice recently," says Claire Skinner, with a little laugh that crinkles her fair-skinned, luminously beautiful face. Over the past year, that face has become quite familiar to television viewers, as, bemused, confused and occasionally amused at the behaviour of her on-screen children, Skinner found herself in the slow-burning hit of 2008, Outnumbered.

If the set-up of the BBC sitcom was predictable – harassed mum and dad given the run-around by their three brats – the execution was a revelation: Skinner and her screen husband, the comedian Hugh Dennis, worked to a script, while the three children were encouraged to improvise their responses. And what they dreamt up turned into some of the most toe-curlingly acute scenes of ineffectual middle-class parenting: Karen, the youngest, turns the simplest conversations into battles of insane logic; her big brother Ben is barely socialised; and Jake, the eldest, despairs at the attempts of his parents, Pete and Sue, to impose anything like order. Few lines are played for laughs, and, for such a high-concept show, the result is both funny and natural, no one more so than Skinner.

Despite the success of the programme (there's a US version in the works), Skinner clearly does not want to be typecast as Mrs Affable. Sweet as she is in person, the 43-year-old is hoping to land flintier parts, following her portrayal of the sourpuss Fanny Dashwood in Sense and Sensibility, Andrew Davies' recent Jane Austen adaptation for the BBC – in a flash Skinner would harden her doe-like prettiness, the lips tightened with avarice. Golden ringlets have never looked more like coiled snakes.

She mentions that she has been thinking about Lady Macbeth, and she is taking the title role in Mrs Affleck, Samuel Adamson's new play which opens at the National Theatre this week. In stark contrast to Outnumbered, this is a modern rewrite of Ibsen's bleak family tragedy Little Eyolf, in which Skinner is a bitterly unmaternal housewife, stuck in a coastal town in 1950s England. An emotionally twisted and sardonic sophisticate, Rita Affleck sidelines her handicapped nine-year-old son while being a desperately possessive spouse, tangled up in a near-incestuous love triangle with her husband, Alfred (Angus Wright), and his half-sister Audrey (Naomi Frederick).

"Playing Fanny Dashwood, who was very spiky, was a lot of fun," remarks Skinner, and she admits that, surprisingly, Mrs Affleck has also reduced her to one or two fits of giggles during rehearsals. "Ibsen has this weird effect," she explains, "which I've heard other actors talk about too. I think it's because it's so madly black, but about four in the afternoon – or after a run-through – everything starts to look terribly funny. I just get a bit hysterical."

Directed by Marianne Elliott (whose previous NT triumphs include Ibsen's Pillars of the Community), Adamson's update promises to be both a harrowing drama and an enjoyable return for Skinner to the stage.

If you've not caught Skinner at the theatre, you may well have seen her on screen in Bridget Jones's Diary, Life Begins or Lark Rise to Candleford – or indeed in two of Mike Leigh's finest films. In Life is Sweet, she created the role of Natalie – the steady tom-boy sibling of Jane Horrocks' monstrously stroppy Nicola – and in Naked, the flustered house-proud Sandra, driven up the wall by a grungy David Thewlis. Leigh himself has described Sandra as "a great comic performance" and one of his favourite characters, endowed with "this wonderful, disjointed way of not completing her sentences".

She found ad-libbing with Leigh delightful, "like playing a giant game for months", though she points out that the improvisational element in Outnumbered works in a different way. "We get through acres of tape, but it's very fast: filming six or seven episodes in nine weeks," she says. "The children don't have a script, but Hugh and I are working from one [provided by the show's creators, Andy Hamilton and Guy Jenkin]. Obviously, we have to deviate from that at points because they [the three child stars] are on a seek-and-destroy mission, and they come out with just extraordinary stuff. You see Guy and Andy whispering to them in a corner, and you know the scene isn't going to go quite how you imagined!"

Also, the children can legally work for only 45 minutes at a stretch, going off for a rest or tutoring. "So often," she clarifies, "when you see shots of Hugh and me, we are in fact acting with Guy and Andy who've got little eyes taped to their chests, so we are acting to the right height."

As a child growing up in Hemel Hempstead, the youngest daughter of a shopkeeper and an Irish-born secretary, Skinner was intensely shy. "It was almost debilitating," she explains; yet she soon discovered that she could break out of her shell when placed in the limelight. "When I was still primary- school age, my brother's football club, called Emerald Vale, had social evenings and – I can't believe I did this – I used to get up and do a whole Mike Yarwood set, before sitting straight back down again." She hunches up mousily, impersonating her infantile self.

"And I was always secretly writing to Opportunity Knocks!" she confesses. "So I was quite an odd creature: this mixture of withdrawn and precocious... It seemed hard [at school] to fit into groups, so I'd go from group to group, a bit of a Zelig type. I just found it easier communicating through acting, being other people, and I still find I can do all sorts of things in character that I can't sort of..." She tails off, then adds that she adores karaoke nights, though she still has to steel herself before bursting into song. In quieter moods, she attends Quaker meetings.

As a teenager, Skinner devoted every spare minute to extracurricular theatrical pursuits, greatly encouraged by the drama teacher at her comp, Mr Clay. Then, racing off to London to train at Lamda, she never looked backed. You can just discern a trace of her south-of-Luton roots – down-to-earth, dropped t's – in her RP accent.

Spotting her potential, Alan Ayckbourn nurtured and pushed the fledgling Skinner to take risks as both a comedienne and tragedienne at his theatre in Scarborough. By the mid-1990s she had won both a Critic's Circle and a Time Out Award, as well as a nomination in the Oliviers, for her fragile depiction of the cripplingly shy homebird Laura in Sam Mendes' production of The Glass Menagerie. It was a part she was born to play. She and the fast-rising Mendes clicked and Skinner went on to be his Desdemona, alongside David Harewood's Othello and Simon Russell Beale's Iago, at the NT.

She was somewhat awed by Harold Pinter's imposing presence when she played the wraith-like daughter in his 1990s comeback, Moonlight. "Sometimes in the room with him [in rehearsals], it seemed almost super-natural. The way he talked about what he had written, it was as if he'd been 'channelled' or something. You had these lines that were really potent, but you didn't quite know why."

As for the future, Skinner will be back on the small screen later this year, in a new ITV2 series called Trinity, set in a gothic university that's rife with bright young things, sex, drugs and murder. "I get to play a don. I don't know how that happened. I barely scraped through my A-levels," she says.

She would also be happy to participate in a third series of Outnumbered if it is recommissioned. The US network Fox is planning a remake Stateside, but Skinner won't be up for that. She is a devoted real-life mother and wants to raise her two sons – aged six and nine – in north London with her husband, the TV director Charles Palmer. She carefully protects her children's privacy, but merrily recounts how she met Palmer when he was a young focus puller on Dance to the Music of Time. "It was day two. I had to take all my clothes off and go and stand behind the camera. And there he was!" she chortles. Not so shy after all, then...

'Mrs Affleck' is in previews at the NT Olivier, London SE1 (tel: 020 7452 3000), opening on 27 January. The first series of 'Outnumbered' is available now on DVD

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