Three years ago in Chalk Hill estate, a housing project in Wembley, 16-year old Louise Harman was spitting loopy rhymes into an old tape recorder and uploading them to Internet peer-to-peer services with hyperbolic ID3 tags as a way to generate homemade hype. These days, other people take care of that last bit. Harman, who goes by the cheeky handle Lady Sovereign, cracked the U.K. Top 40 this past summer with a thrilling single called "9 to 5" (not a cover), and is expected to be the stubborn, impish voice that finally brings British rap to American airwaves.

If you feel like you've heard this all before, it's because you have. Since the 2002 release of The Streets' Original Pirate Material, record labels have been struggling to find a U.S. market for these British club hits. It's been a bit of an uphill battle. In an attempt to drum up a quick story angle, artists like Dizzee Rascal and Wiley are often incorrectly branded "British rap" when they're actually part of a subgenre called grime. Grime grew out of a strain of British club music known as garage and is a culture unto itself, rather than just an attempt by East London ruffians to mimic Yank posture and cadence. Without some level of familiarity with that evolution, grime's warped synths and glottal flow can sound harsh and uninviting—especially when it's flippantly associated with hip-hop. Though the recent prominence of Southern rappers like Young Jeezy and Paul Wall, who themselves build songs from doomy, minor-key synth lines, might end up removing some of grime's foreignness, in America the music still exists only on the fringes of indie rock.

Lady Sovereign is being groomed for bigger things. Pursued and signed by Jay-Z himself to Def Jam (after a nerve-wracking audition in which she had to freestyle in front of him, Usher and L.A. Reid), Sov reportedly received a seven-figure advance with only a few singles to her name, none of which had been released in the U.S. Though the just-released Vertically Challenged EP—which compiles most of those early singles—does bear a few traces of grime's clamminess, advance tracks from her forthcoming full-length find her playing a coy game of footsie with conventional pop. The brisk, buoyant "9 to 5" is built around a seesawing ska organ and a nimble, pirouetting piano figure, sounding like the last great Eminem single before 8 Mile and Triumph the Insult Comic Dog turned him all sour and serious.

Where other British MCs are hamstrung by colloquialisms, Sov's lyrics have the bravado and irascibility American audiences have come to expect from rhymesayers. MIA's canny and nimble deployment of signs and signifiers was a big hit with critics who enjoy fucking up good pop music by overanalyzing its construction (and, OK: guilty as charged), but it has yet to find a significant audience outside those circles. Sov's songs have less to decode and, as a result, pack a greater visceral thrill. They're funny and scampish and have the kind of joke-a-second construction that rewards repeated listens. She fiddles with her delivery, hardening her "th"s to "d"s to sound more like a dancehall toaster than a Wembley MC.

The songs are also proudly and ruthlessly working class. Last year saw the rise in Britain of the snide classist slur "chav," used to denigrate people for their perceived lack of education, coarse speech and style of dress. (For point of reference, the Web site www.chavscum.com classifies Eminem, 50 Cent and Christina Aguilera as chavs.) The mania has led to the banning of hooded sweatshirts in some upscale shopping centers, fearing the presence of the garment will "attract the wrong element." Sov shot back quick with a spry pop number called "Hoodie," defending her own dirty-nail status while quipping: "Your granny-fied curtain designs/ Hurtin' my eyes/ You should revise your dress sense before you walk on by."

If there's one key element missing from Sov's songs, it's unchecked reveling in her sudden rags-to-riches transformation. On "Thug Motivation 101," Young Jeezy proudly roars, "I used to hit the kitchen lights/ Cockroaches everywhere/ Now I hit the kitchen lights/ Marble floors everywhere." Maybe Lady Sov is still too connected to her early days in Chalk Hill to get puffed up about her bigger bank account. Or maybe, having viewed the long line of those who have gone before her, she's still a bit skeptical.

Lady Sovereign performs Thu., Dec. 1, 10 p.m., $8, with DJs Diplo and Dave P., Silk City, Fifth and Spring Garden sts., 866-468-7619, www.r5productions.com.