She is an actress with a chameleon-like ability to swap accents, he is a writer whose work is anchored in his native Belfast. Together, they are on stage at the Donmar
ACTORS fall into two broad categories: those who play themselves and those who play other people. One type gets recognised in the street rather more than the other. Last year, while Lynda La Plante's Trial and Retribution was being screened, Helen McCrory found herself dragged into a pub debate about the moral issues thrown up by the series. "I assumed arrogantly that this conversation had been sparked off by the fact that they knew who I was. They asked me my opinion and I realised after about 10 minutes they had no idea."

You can see why. McCrory is currently at the Donmar in In a Little World of Our Own, a new play by Gary Mitchell in which she puts on an Ulster accent to play a born-again Christian in the heart of Protestant Belfast. In Stand and Deliver, a BBC film by Les Blair, she plays a feckless English photographer in Glasgow. In The James Gang, a road movie directed by Mike Barker, she's a Scot who fetches up in Wales. The Donmar play opens the theatre's annual "Four Corners" season: it sounds as if McCrory could play all four corners herself.

If this nomadism has a name, it's character acting. It may be too elastic a connection, but it's worth noting that McCrory is the daughter of a Glaswegian diplomat and a Welsh physiotherapist who spent her childhood moving from Scandinavian pillar to African post. Her accent is pure English girls' boarding school (with a nicotine flavouring) although, with her wide, dark eyes and four-square Celtic bone structure, you can't see her wielding a lacrosse stick. She has got through most of her twenties without playing the love interest, unless you count Nina in The Seagull (at the National with Judi Dench).

For her most prominent leading role so far, in the BBC's hard-hitting Streetlife, she bleached her curls blonde and donned a Welsh accent to play a dpregnant single mum on a grim Cardiff estate. She was next found up at the other end of the social map, as a surgeon's repugnantly ambitious daughter (alongside Ian Richardson) in The Fragile Heart.

"If you're willing," she explains, "to have the same expectations of yourself that many male actors have - and many women actors deny themselves by wanting to look sexy or pretty - then there are a lot of parts that are open to you. If there's one interesting thing about acting, it's trying to lose your ego in the character."

In a Little World of Our Own is McCrory's first stage role since Les Enfants du Paradis, Simon Callow's epic calamity at the Barbican. "They panned us," she says of the critics. "It was a very long show: people came with bumfluff and left with grandchildren. It was one of those real cliches: in the rehearsal room, everybody was completely behind it; and when it came on to the stage, it was a big aircraft hangar and the staging really didn't help the play."

That experience was presumably one of the spurs that made McCrory take the rare step, at least among stage actors, of jointly starting her own company. Her mild dyslexia notwithstanding, she now has to read even more scripts than she would as an actress. In its first year, her company, named The Foundry, has helped mount four new productions, including Neverland by Phyllis Nagy at the Royal Court. In a Little World of Our Own, a busy thriller that has already won Gary Mitchell the "Best New Play at the Irish Theatre" award, meets all The Foundry's criteria.

"I wouldn't say it's a backlash against this new wave of young playwrights," McCrory says, "but you go and see their plays and say, `Yeah, that's what I thought when I was 16. But I'm 28 and I don't really want to cut off half my brain in order to understand your writing.' Also a lot of plays are really TV plays or poems, but they're not theatrical. We talked to a lot of literary agents about the fact that we wanted to do conventional, well-crafted plays that are about something, aren't just sexy with lots of guns and sensationalism. It's fashionable and therefore transient and what's the point in doing them?"

The point of doing the BBC film Stand and Deliver, about a London stand- up (Phil Daniels) who does two gigs one weekend in Glasgow, was to spend four months in Glasgow working with writer-director Les Blair, whose working- method bears comparison with Mike Leigh's. There's a rambling, inconsequential feel to the piece, occasioned by Blair's refusal to deliver anything as staid as a plot that stands on its own two feet, but McCrory is delightfully kooky as an artistic butterfly of independent means.

Blair went through the laborious process of constructing a character with each actor "so you don't just end up playing yourself in Glasgow doing a different job. It takes a lot of balls to do that because there is no security there, there is no safety net. I spent my first few weeks thinking, what happens if nothing we come out with is of any interest to anybody?"

It was in a similar spirit of curiosity that she took the screen role of a whore who is bitten by Tom Cruise in Interview with the Vampire. "I wanted to see how a studio film works. It literally is, `Mr Cruise will be on set in 60 seconds ... Mr Cruise will be on set in 30 seconds ... Mr Cruise is walking on set.'" And was it forbidden, as rumour alleges, to look him in the eye? "I wasn't told not to. We had a rehearsal the night before, after he and Mr Pitt had finished filming, and no, he was completely normal. I was doing The Seagull at the time, and he said, `I hear you're doing The Seagull, I'll try and come and see it.'" (He didn't.) And how tall is he? "Taller than me. But most seven-year-old children are taller than me."

`In a Little World of Our Own' opens 8pm tonight, Donmar Warehouse, Earlham Street, London WC2 (0171-369 1732).