“I ain't stupid, you can count my As,” rapped baby-faced musician Jahmaal Fyffe, aka rising grime star Chipmunk, on his single Chip Diddy Chip. He was referring to the five he bagged in his GCSEs — and now the 18-year-old Tottenham resident is feeling the strain of his A-levels.

He is currently studying for his exams in drama, sociology and critical thinking at Haringey Sixth Form Centre — and yet between revision sessions, he has found the time to sign a major label record deal and rap on a hit single.

“I've got grey hairs, man,” he tells me, 24 hours before his next sociology test. “I've even started drinking coffee. There's no time to breathe.”

It's a prudent move to complete his studies despite the obvious distractions — fellow pupils already ask him for his autograph and film him on their mobile phones through classroom doorways. But still, he won't have much longer to wait until he is a full-time celebrity.

Once the exams are out of the way, he will play Glastonbury on 26 June and Hyde Park's Wireless Festival on 5 July. Then, on 19 July, he appears alongside The Wombats and Ms Dynamite at Somerset House as part of What Next, a new event specifically for 14 to18-year-olds. That's just after the bouncing ska of his next single, Diamond Rings, should have become his next hit.

It's a pure pop song, a significant step away from the grittier sound of his earlier tracks, such as Beast and Who Are You? It will see him join other London acts who have moved from the urban underground to the mainstream, such as DJ Ironik, whose lively updating of Elton John's Tiny Dancer featured vocals from Chipmunk and got to number three last month.

Then there's Camden R&B trio N-Dubz, whose album Uncle B is a little-heralded platinum seller, and Bow rapper Tinchy Stryder, whose collaboration with N-Dubz, Number One, did indeed hit number one for three weeks in May. Even the acclaimed grime pioneer Dizzee Rascal, who won the Mercury Prize as far back as 2003, had to become significantly more accessible to achieve his two number ones, last year's Dance Wiv Me and the current favourite, Bonkers.

“The scene has changed, a lot of underground people have gone overground,” says Chipmunk, who advises keeping an ear out for Mz Bratt and Scorcha next. However, unlike the last time UK urban musicians started scoring real hits, when So Solid Crew emerged in the early part of this decade, now there is not the spectre of behind-the-scenes violence. “There ain't no rivalry,” says Chipmunk, “we're all mates” — mates who will gladly appear on each other's records.

Chipmunk's debut album, I Am…, will arrive in the autumn on Columbia Records, a year since he became the youngest ever act to win a MOBO Award, despite being unsigned at the time. “That was yet another thing I didn't expect. It's all been pretty wow-ish.”

Those feet still seem to be firmly planted on the ground, though. He recently pulled out of a celebratory gig at the Forum on the last day of his A-levels as he couldn't find the time to practise. “Now I'm going to go and see Transformers 2,” he tells me. “And sleep.”

What Next, 19 July, Somerset House, WC2 (0844 847 2317, www.whatnext event.org.uk), www.myspace.com/chipmunkartist

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