You may have met these two somewhere before

I swear to God I used to know an Annie. Lynda Steadman, in Mike Leigh's new film Career Girls, is dowdy and tiny, dwarfed by asexual, voluminous clothing. She tugs a gingered forelock over anxious, downcast eyes, hunches and cringes, her fingers stealing up to cover her mortified face. A quick chat with the actress quickly establishes that she couldn' t have met my "Annie", and anyway, the fascination of Mike Leigh characters is that they are unique individuals while nevertheless remaining members of a recognisable type. Probably everyone who went to college in the mid-Eighties knew an Annie: the dyed, asymmetrical Cure fan's haircut, the unhappy-with-my-body rusty black garb, the arsenal of nervous tics and itches, the timid baby voice.

Career Girls is a quiet chamber piece for Leigh, after the crowd-pleasing Secrets and Lies. Its surface simplicity is belied by a complex structure with two interlocking timescales. A vindication of female friendship, it covers a weekend over which two former college friends - the now groomed and grown-up Annie and Hannah (Katrin Cartlidge) - meet up after years apart. A northerner and a Londoner, they first met as students at a London Poly. Edgy, unpleasant Hannah was never the obvious soulmate for mousy doormat Annie. But over the weekend, they recall why and how they came together in the first place.

We meet on a hot night in a Waterloo coffee-bar, round the back of the National Theatre where Cartlidge is taking part in a workshop. With her nervy grace and darting black eyes, Cartlidge is unmistakable from films such as Naked and Breaking the Waves; Steadman (no relation to Alison, by the way) has sloughed off the carapace of gloomy, pallid Annie to return to her native condition: forthright Belfast accent, clothes which accentuate a petite figure, and a sheen of health. Cartlidge is the more cool, thoughtful and analytical; Steadman more emotional, warm and direct.

Leigh is unusual in that he shoots in sequence; indeed it's hard to see how he could have done otherwise, so stark is the contrast between the gaucheries of youth, and the superficial maturity of adulthood. The situation (there isn't much of a story) poses all kinds of questions about the possibility of change and the development of personality. Annie and Hannah, for all their faults, are survivors. It's finely done.

Still, the Eighties scenes are startling to watch as hyperactive Hannah yaps and barks, and Annie, whose Goth face is patched with eczema, scratches distractedly at her cheeks, sniffs, mopes and rolls her eyes. Another flatmate, Annie's fellow psychology student Ricky, moves in. Dismayingly, he too is a wounded soul with bewildering speech patterns, and his own panoply of face-pulling and gesticulation. Bark, twitch, scratch, itch, mumble: there's been nothing on screen quite like this orchestration of dysfunction.

Suggest that they might all have gone a little over the top, and Cartlidge pounces. "Well, you say you knew an Annie. Someone else will look at Ricky and say, `God, I definitely know him', so I don't know that they are extreme. We're just not used to seeing that in the cinema. You're always told: you don't move a muscle in your face, everything has to be very interior, all you have to do is think, all you have to do is be. That's one school of film acting. The result is sometimes a little bit of vanity for the actors: it means they never scratch their head or pick their nose. We're not used to seeing those mannerisms which ... push the edges of the frame. But when you do see them, it's amazing; it's like watching Van Gogh use colours that were never used before to describe a tree. Whoever heard of a blue tree? The fact is, trees are blue, but you have to see it through the eyes of a Van Gogh."

Ricky's fate is left open: the gulf unbridged between the troubled but essentially kindly adolescent and the broken man the women later meet by accident. "It's awful, just awful," whispers Steadman, her eyes filling with tears. "Only he knows, only Mark Benton [the actor] knows. I still get upset when I think about his character. I'll tell you, when Annie and Hannah bumped into him after all those years, it was just ... I haven't words to describe it. Gut-wrenching."

While Mike Leigh's famous improvisational method has created a stunning depth of emotion in these three main characters, an emotion that the two actresses at least find difficult to throw off, the same cannot be said of the smaller roles. The women's relationship is the film's bedrock, but they pit themselves against an array of glib, sexist, Mike Leigh male stereotypes, from the coke-sniffing broker whose penthouse flat the women pretend to be interested in buying, to the smooth estate agent who remembers Hannah from college, but not Annie, whom he actually slept with. The men are more humorously treated than comparable types in Naked, but just as crassly misogynist.

Cartlidge: "But these are the men those women attract, and they're both aware of that; they question why men like that are orbiting around them. There are all sorts of reasons why Annie and Hannah are attracted to these men, because of their own backgrounds."

Steadman: "I read in a review that this journalist had really enjoyed the film, but they'd thought it was going a bit over the top when you go into the yuppie's flat and there's the porn mag on the bed, and the false tits in the kitchen and the nude woman mural on the stairs. That's absurd! I'm telling you, I've known stockbrokers, and that's exactly what their flats are like."

Despite the irritations of minor characters and contrived twists, the film's strength lies in the emotional truth of the central relationship. Cartlidge: "With Hannah, nobody can put up with it for very long, and the only person who doesn't go, 'Excuse me, what did you just say?'is Annie, and that's because she can see past the armour. They share a very similar background, a split home, which they discover in the kitchen-sink- ronicity of the early years ..." Steadman: "But Annie also tolerates Hannah for another reason: it's just in Annie's nature, she's just so soft, she's very giving and ready to take the blame for anything that happens in her life."

"There's yards of cloth that isn't in the suit," Cartlidge says. So do they know where their characters were brought up, went to school, what their formative experiences where, how they lost their virginity? They chorus: "Oh God, yes, yes, yes, yes." Steadman: "Everything." Cartlidge: "Because obviously the more you know, the more you can put on the table. I sometimes felt I didn't have the energy to play Hannah. To be that hyper constantly was exhausting -"

"Well, I would never have known. Katrin's saying this, but it certainly never came across."

"- As soon as Mike said, come out of character, I nearly collapsed."

"For my part," says Steadman, "the exhaustion came from the physical feat of rolling my eyes and walking the way Annie did with her head down. I had a constant sore leg."

Cartlidge is a Leigh veteran, but you get the impression that Steadman, whose film debut this is, has a few reservations. Asked if she'd repeat the experience, she pauses - "Errrr" - and laughs. Finally she says slowly: "It was a unique experience, and if Mike turned round and said, `D'you want to be in my next film?', how could you possibly say no, when it's just an amazing experience. It's gruelling, but very rewarding, because the actors are given the chance to have a lot of creative input." She laughs again, with the relieved air of someone who's pulled off a tricky, diplomatic answer. Cartlidge joins in the secret joke, before saying apologetically, "The paint's still wet. It's so intensive, it takes a long time to get away from the experience."

! `Career Girls' (15) opens on Friday.