Too silly for words... ...too gorgeous to be true

There are two problems in Julia Sawalha's life. One is that people tend to confuse her with Helena Bonham Carter. They show her to her rival's chair (and vice versa) at awards ceremonies. The second is that she was born too late. Quite soon after you first meet her, you realise that she is, in fact, an unreconstructed Sixties chick masquerading as a Nineties actress. Everything about her - her hair, her opinions, her passions, her spare-time activities, her maquillage, her jewellery - even her taste in music - all yell "Sixties!" at you. If ever there was a girl born to have a bunch of marigolds drawn in biro on her upper cheek, Ms Sawalha is it.

Which is odd, given that her fame still rests largely on her portrayal of a straight-laced teenager with nothing but contempt for Sixties culture, as expressed in the clothes, habits and vocabulary of her mother. Saffron and Absolutely Fabulous returned to the nation's television screens last week, to confirm that there's no prig like a female prig, and no one who can embody one better than Julia S.

Another side of the actress can be seen next weekend, when Channel 4 presents McLibel!, Dennis Woolf's three-hour reconstruction of the three- year courtroom jousting tournament between the McDonald's burger Leviathan and the two London anarchists, Helen Steel and Dave Morris, who dared to say rude things about them. Sawalha plays Steel as a sullen, endlessly sceptical figure amazed to find that she may have right on her side after all.

Between these embodiments of scorn, she has taken to costume drama like a duck to l'orange, playing the hoydenish, soldier-mad Lydia Bennett in Andrew Davies's adaptation of Pride and Prejudice and the put-upon Mercy in Martin Chuzzlewit a year earlier. "I like the way everything swings back and forth in this job," she remarks. "One minute, I'm looking after a boozy mother in a modern comedy, the next I'm being beaten around the head by Keith Allen in a Dickens novel..."

So when you meet her you're prepared for a bit of a shape-changer, a sophisticate, a wary, eyebrow-raising ack-tress. Instead, you get a voluble gigglepuss with a Sarf London accent and a sensibility that's closer to Biba than Prada.

Sawalha is, shall we say, a surprise. Nothing you have seen, on small or big screen, prepares you for how amazingly pretty she is in the flesh, her completely round, doll-like face surmounted by a Medusa jungle of chestnut curls that cascade over her brow. Her eyes are piercingly grey- green and their whites shine like Martin Bell's best suit. Her long eyelashes have an unearthly, tarantulan quality that you might ascribe to art rather than nature, except that nothing about Sawalha appears to be false.

She is, it turns out, a vegetarian, an environmentalist, a feminist and a poet; but also a drinker, a smoker, a good-time girl and a chatterbox of appealing indiscretion. Nobody who can be so many contradictory things is trying to sell you an image of themselves. She sports a silver bracelet and three rings, with another one, set about with runic Eastern symbols, on a chain around her neck. And she laughs a lot, like an exhibit in a demonstration of hysteria before Victorian medical students. She seems, by turns, too silly for words, and too gorgeous to be true. Why had she wanted to play Helen Steel? Was it a personal crusade? "Yeah, definitely. When my agent rang me and said the words Greenpeace and McDonald's, I didn't have a clue about the McLibel case; but when I met Dennis Woolf, I thought, I've got to support this. I was a Greenpeace supporter already, and then I found that London Greenpeace is just five people and I got really interested." As the world knows, in 1985 the quintet were distributing leaflets (headed "What's Wrong with McDonald's?") laying several accusations at the hooves of the beef giant: that they tortured animals, caused food poisoning, exploited staff, sold food linked to cancer and heart disease; and, for good measure, that they were destroying the rainforests. McDonald's tracked down the leaflet's perpetrators and served libel writs on them. Three apologised; Steel and Morris didn't. The ensuing trial was expected to last three or four weeks; instead it dragged on for a record 313 days. "I really admired the story of their struggle not to be silenced," said Sawalha. "I hadn't had the time or the chance before to use my name to help. . . I believe in people saying what they want if they believe in fighting a cause."

Could she have become involved in a different cause? Say, the Bridgewater Four? "No, there's something special about attacking big corporations - and especially McDonald's". What had she got against McDonald's? "It distresses me when I take my seven-year-old nephew out. I cook healthy food, and he wants to go to McDonald's. He doesn't even like the food, he just wants the toys, the Happy Meals. I can't stand to see people walking down the street eating fast food."

On the face of it, I said, the role didn't offer a lot of scope for an actress, being confined to long periods in the defendants' box looking cross and saying "Yeah?" to the snooty QC with her hands in her jeans pockets. "Not at all," said Sawalha, "it was a challenge because you had to play it down so much. It's very hard to dramatise something factual and not make it look overdone; but also not to make it look so under-dramatised that it's dull."

Sawalha has been a keen environmentalist for years, since she went to Windsor Great Park and watched, unsmiling, as Winnie the Whale and friends cavorted for the audience.

"It was so distressing to see the dolphins banging themselves up against the wall, having to perform. It disgusted me." She is a fan of the ineffable Swampy, is deeply suspicious of the judiciary system and has little faith in the New Labour dawn. "I think they're all as bad as each other. And I didn't vote last week. I was going to vote for old Tony, but to tell the truth I lost my voting card. I was running round, a tiny bit pissed, at half past six in the evening..."

This Bridget Jones side of her nature can be either grating or enchanting, depending on your point of view. Julia Sawalha radiates a kind of wayward innocence, a girlish helplessness that would bring out, I'm afraid, manly- protector instincts in the most new-mannish of New Men. In her spare time, she says, she writes poems, sets them to music and plays them on the guitar. She likes Fleetwood Mac and Led Zeppelin. Her favourite book appears to be a teenage novel called My Darling, My Hamburger. I watched in fascination as she extracted a Silk Cut, nipped off the final couple of centimetres and lit up. Excuse me, I said, but why...? "I'm giving up smoking. I only smoke down to there..."

She is, as her surname gives away but her complexion does not, half-Jordanian. She grew up in Upper Norwood in south-east London. Her father Nadim is an actor (he plays the wise and chortling Dr Shaban in Dangerfield). Nadim created a Bedouin tent affair, made of satin, in the family dining-room, "and we would have feasts, with singing and dancing, with lots of arak, which is like ouzo and we were allowed to drink it because it was medicinal". Her mother is "from Surrey - completely". Was she aware of being different from her schoolfriends? "Only from people saying things like, 'You're dirty, 'cos you're an Arab and you eat with your hands.' And I'd go home and say to my Mum, 'Are we dirty?' And she'd say, 'Tell them Arabs are a damn sight cleaner than any of them.'

But I grew up very proud of my culture and very happy to have, you know, two sides..." Was her father a Muslim? "No, he's a Christian. A spiritual man. But he never pushed any belief on us. When I was nine, I asked what God was, and should I believe in him and they said, 'If you want to pray at the end of your bed and believe in something up above, that's up to you.' She considered the alternative route her life might have taken. "If I'd been a Muslim, I wouldn't be sitting here now." Where would she be? "I'd probably be an archeologist in Jordan." Wasn't it more likely she'd be married off to a Jordanian businessman and stuck at home dressed in a chador, minding the children and never going out? "Yeah, probably. But I'd still be diggin' around in my back garden."

God forbid. Sawalha decided for herself on an acting career at the tender age of 10. She went to the Italia Conti stage school. "I'd always gone to dance classes, while my sister went to full-time school. They seemed equal options. Everyone was going off to ordinary school and I just thought, I'd like to sing and dance for half the day..." On the first day, she found herself in acting class, sitting in a circle and being told that a lump of invisible magic clay was being handed round, which she had to transform into something.

"And you watch this thing coming round, and your imagination is going bonkers, and suddenly it gets to you and something happens, you perform, you do something because you have to. And I felt so satisfied afterwards. I've always had to confront my fears." Did she still get fearful? "I'm going to Manchester next week, to the Royal Exchange, to appear in The Illusion by [she consulted her right hand where the details were written at the base of her thumb] Pierre Corneille, adapted by Tony Kushner. I'm quite terrified..."

Sawalha has yet to play the kind of full-on, explosively "unrestrained" leading lady she is clearly capable of playing. She sweetly confesses to being "a vamp in my own time, my personal time". Her forays into clubland tended, in the past, to coincide with her relationship with Keith Allen, a legendary Groucho habitue. "The last time I was in the Groucho, I woke up in the morning and my finger was all black and blue, and bent back. I couldn't work out what I'd being doing with it. And I'd left without my shoes. It's just not good for me to frequent such places. It's funny," she said as a random thought struck her, "I grew up beside Crystal Palace, now I live beside Alexandra Palace, and they're the two highest points in London."

It must be the muezzin in your soul, I said smartly.

"What's that?"

A muezzin? A man who climbs to the highest vantage point in the city and calls the faithful to prayer.

"Oh," said Sawalha. It's another adorable trait of hers, not knowing things. I asked her what she thought of Ellen, the scandalous, Oh-my-god- she's-a-lesbian American sitcom. "I've never seen it. What is it?"

It's one of those Channel 4 imports, I said. Like Seinfeld."

"What's Seinfeld?"

And she means it. She's never seen Cheers or even Friends. Speaking of friends, I asked if she ever hung out with the two actresses with whom she must contest the period-costume territory in the future, Helena Bonham Carter and Kate Winslet. "No, I've always stayed away from other people in my profession. I've met Kate a couple of times. In fact, I lent her my bra once for a photo shoot." Come again? "She had a very see-through top on and I said, 'You going to be photographed like that?' and she said innocently, 'They asked me to.' I said, 'I'd put something on under that if I were you,' and she said 'I haven't got anything'. So I lent her my bra. I never saw her again." A thought struck her. "I never saw my bra again, either." And the divine Ms Sawalha goes off into another (surely terminal this time) fusillade of giggles.