Lisa from the Simpsons squeaks up about sexism

"What I hate," says Lisa Simpson, sister of cartoon tearaway Bart and daughter of Marje and Homer, as children clothed in Simpsons' merchandise struggle to sit on her knee, "is that I don't get any catchphrases. Bart gets 'Eat my shorts', Homer gets 'Doh!' What do I get? Nothing. And I don't get any of my own merchandise. I'm not on any T-shirts or mugs or anything. I mean, f--- off . It's so sexist."

Unnervingly, the voice of Lisa Simpson, the family genius, is emanating not from a small yellow cartoon child with bulging eyes and triangular hair, but from the body of Yeardley Smith, the 33-year-old actress from Washington DC who has made the part of Lisa her own. But it doesn't sound very different.

This is the third wave of The Simpsons' British invasion. First they came by satellite, building a cult following on Sky of at least 1 million viewers for every new episode; then they went terrestrial, first on BBC1 and then on BBC2, with audiences of 6 million.

Now Lisa/Yeardley is over here "in person" to promote the sale of original art from the series at the Animation Art Gallery near London's Oxford Street, which opened yesterday. Such is the extent of Simpson fever this side of the Atlantic, that by mid-week most of the hundreds of animation frames, or cels - costing from pounds 195 for "The Simpsons Couch Gag" reproduced from the opening credit sequence, to pounds 550 for a cel from the cult "Roadkill 2000" episode - have already been sold.

Seven years ago when Yeardley Smith (Yeardley is her dad's middle name, which he foisted on his daughter) went to read for The Simpsons, she saw it as just a small- time cartoon series audition.

"It was the easiest job I ever got," she says in a high-pitched voice just a few tones lower than Lisa's. "The casting director called in a bunch of people she knew had interesting voices. Nancy Cartwright [the voice of Bart] was there and I read for Bart and she read for Lisa. Then we swapped and that was it." Lisa's smart-alec character came quite easily, she says. "I'm naturally sassy."

The secret of The Simpsons' success, Smith believes, lies in its subversive content and its ability to appeal simultaneously to children and adults. "A lot of American sitcoms are pretty cheesy," she says. "But we can say anything because it's a cartoon."

Matt Groening, the yellow-trash family's creator, has used the series deliberately to "wind up Republicans" with allusions to right-wing policies edited in at the last minute. He has been so successful that George Bush once used his State of the Union address to criticise the show.

In a nation where comedy more usually takes a self-righteous tone exemplified by the heavy moralising of The Cosby Show, the satirically dysfunctional and often bittersweet world of Springfield came as a blast of fresh air.

Celebrities flocked to join the cast of voices or to appear in two-dimensional Simpson-land. "For some reason," says Groening, "a lot of Hollywood bigshots are curious to see how they'd be drawn with bulging eyes and no chin." Top Hollywood names fought to speak the first word of The Simpsons' baby Maggie, who had previously only made Hoover-like sucking noises.

Elizabeth Taylor eventually won the contract to say just one word: "Dada." But Smith has another version of the "first-word" saga. "That is just bullshit," she says. "Months before Liz Taylor came along I said Maggie's first word and it was 'spaghetti'."

Success, however, has also brought imitations including the mindless, sex-obsessed Beavis and Butthead with their trademark dirty giggles.

More recently the series has spawned a serious rival in King of the Hill, an intelligently understated cartoon set in Texas and starring Hank Hill, a white-trash propane gas salesman with a Homer-like paunch and nightmare family. The series' production team includes both Mike Judge, the creator of Beavis and Butthead, and Greg Daniels, who has written for The Simpsons and the sitcom Seinfeld.

Following the showing of the King of the Hill pilot episode on Channel 4 last week which reached 2 million viewers, playgrounds and dinner parties have been divided over which cartoon is the most cutting-edge. But Smith says the Simpson team is not worried about the Hill phenomenon.

"The best way to sum up the rivalry would be to say that we don't really care," she says. "We'll take on anybody, but it's like there's us, there's you, have a nice day." Or, roughly translated into Simpson-speak: "Hank Hill, eat my shorts."