Sarah Silverman, Hammersmith Apollo, London

Filthy irony and dark, dirty comedy take on our taboos

"I have had an abortion. Abortions. And obviously it's, like, one of the top 50 hardest decisions a woman can make." It's for lines like this, an opener last night at her first stand up gig in this country, that Sarah Silverman has been called "the world's most outrageous comic". At 37, with a glittering television career and a nice sideline in viral YouTube clips (this year's "I'm Fucking Matt Damon", won her two Emmys), Silverman is the pre-eminent American female comedian of her generation.

If you haven't seen it before, Silverman's mode is one of filthy irony. Dirty and dark comedy, taking on taboos of race, sex and religion, is undercut by her appearance (attractive) and an almost unbearably cutesy delivery: with wide eyes and innocent expression, the caricature of a Jewish-American Princess, Silverman appears to endorse bigotry of every shade, an edgy approach that has shot her to stardom in the US. The question hanging over a Silverman performance in the UK was whether she would be offensive enough for the famously less squeamish Brits.

She does her worst. "Scientology is so gay," she starts off with a goofy smile, "And, I don't mean that in a bad way. When I say gay, I mean ... retarded." There were jokes about the distended stomachs of starving Ethiopian babies; rape ("I wish I had the power to rape somebody. I know that sounds dark. But I'd like to have that power – and choose not to use it."); of Barack Obama, whom she endorses, she says she's concerned America might not elect "a half-black" president. "Oh, know what, I shouldn't be so pessimistic... He's half white!"

And that is Silverman's conceit: these quips aren't about race, but racism itself – and, specifically, the subtly hypocritical ways in which liberals attempt to negotiate those subjects. Her jokes are discomforting. But not always laugh-out-loud funny.

The laughter is tempered when lines are recycled from recordings of stand-up shows (her favourite one about it being bittersweet for a Jewish girl to be raped by her doctor only getting a titter) and television appearances. Her heart, you sense, is not in live performance.

Half a dozen songs, with Silverman accompanying herself on guitar, were a mixed bag of new numbers and older ones, including her cruel ode to geriatrics, "You're gonna die soon/we're all gonna die some time/but not as soon as you guys."

The fresher territory that brought the belly laughs was her gynecological material. A pretty, ponytailed woman, dressed in a short girlish skirt experimenting with ways in which she can make the word "pussy" sound more offensive "cause, it's just not gross to me any more," is, I found, bizarrely amusing. She blows out her cheeks, enunciating the word repeatedly, trying a lisp, then a tongue roll: "puth-hee". She smiles. It's the kind of puerile humour last heard at the back of double chemistry, but it reduced this former schoolgirl to uncontrollable sniggers.

And that's Silverman: the funniest girl in the class, whom you want to be friends with for fear that otherwise she'll devastate you with a cutting line.

She concludes: "I'm trying to be ridiculous and silly. Whether you're black or Asian or white – but only those three – it doesn't matter, we're all the same inside." Despite the fake reassurance, Silverman ends up offending her audience anyway, since after barely an hour onstage she announces, "that's it, I've shot my load". For her British fans, enjoying a rare chance to see one of the hottest comedians working today, it was rudely premature.