Sarah Silverman has a reputation for being offensive, but it wasn’t her poop jokes or ironic racism that caused such a smell at the end of her first British headlining gig on Sunday night. The American comic had performed for just 50 minutes. No crime at a smaller, cheaper London venue such as the Soho Theatre. But at this 3,500-seater, where it takes almost that long to queue for the bar, where stalls tickets were £45 a pop, it was larceny.

OK, it wasn’t Silverman’s fault that her support act, Steve Agee, fell ill. Maybe it wasn't her fault that the show was preceded by a five-minute clips batch from the new series of The Sarah Silverman Program (gee, thanks). But it was she who later greeted her fans’ demand for more material with enough ill grace to make you wonder if the mock-narcissism of her comedy persona is as mock as all that.

“F*** this,” she muttered with smiling disbelief as she returned, already changed into her post-show slippers, “It was a great show.” Well, yeah, it was pretty good. Silverman, I’m working hard to remind myself here, is a sharp-minded comedy original. She knocks everything she mentions, from claiming she follows the Kabbalah - “I just feel so much better... than you” - to wanting to adopt - “somebody brown: otherwise you don’t get credit.” Hey, she even knocked our chewy-voweled, merry-old-English accents. Everyone’s a target.

Gag by gag, she plies boorishness and salaciousness with the same coy charm: “I don’t care if you think I’m racist. It’s honestly more important to me that you think I’m thin.” This Jewish comic wonders why Jews and Palestinians should hate each other: “They’re both brown and pushy.” Her strummed songs are tuneful and adorably nasty. They are also, like a lot of her set, familiar from her concert film, Jesus is Magic.

Silverman is sort of herself, sort of a character. And after a while you want something genuine. You want to know what she really thinks, not what she thinks she can get away with. Without more of a moral backdrop, all this saying the unsayable can play as facetiousness sent to college.

She knows the limitations of her arrogant-ignorant persona. But she’s not used to having to explain herself. As she stalked the stage, appearing to resent her crowd for wanting more, it was the eggiest end to a comedy show I’ve ever seen. Edging back to the wings with a mock-grandiose bow, it was the usual petulance but without the usual inverted commas. She blew it.

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